Improve the main README

README.md

-# ngx_http_voms_module
+# `ngx_http_voms_module`
 
 [![pipeline status](https://baltig.infn.it/storm2/ngx_http_voms_module/badges/master/pipeline.svg)](https://baltig.infn.it/storm2/ngx_http_voms_module/commits/master)
 
 ## Description
 
-*ngx_http_voms_module* is a module for the [Nginx web server](https://www.nginx.org/) that enables client-side authentication based on X.509 proxy certificates augmented with VOMS Attribute Certificates, typically obtained from a [Virtual Organization Membership Service](https://italiangrid.github.io/voms/) (VOMS) server.
+`ngx_http_voms_module` is a module for the [Nginx web server](https://www.nginx.org/) that enables client-side authentication based on X.509 proxy certificates augmented with VOMS Attribute Certificates, typically obtained from a [Virtual Organization Membership Service](https://italiangrid.github.io/voms/) (VOMS) server.
 
-The module defines a set of [*embedded* variables](#embedded-variables), whose values are extracted from the first Attribute Certificate found in the certificate chain.
+The module defines a set of [*embedded* variables](###embedded-variables), whose values are extracted from the first Attribute Certificate found in the certificate chain.
 
-## Installation
-
-The generic installation instructions are:
-
-```shell
-$ cd nginx-x.y.z
-$ ./configure --add-module=/path/to/ngx_http_voms_module
-$ make && make install
-```
-
-The module is written in C++, using features from C++14 that are supported by gcc v. 4.8.5 (the version available in CentOS 7) enabling the option `-std=c++1y` (see [`config.make`](config.make)).
-
-A Docker image is available for use in the context of the StoRM2 project, where the OpenResty distribution is used:
-
-```shell
-$ docker run --rm -it -v /path/to/ngx_http_voms_module:/home/build/ngx_http_voms_module storm2/ngx-voms-build
-$ cd openresty-x.y.z
-$ ./configure ${RESTY_CONFIG_OPTIONS} --add-module=../ngx_http_voms_module
-$ make && make install
-```
-
-## Embedded Variables
+### Embedded Variables
 
 The module makes the following embedded variables available for use in an Nginx configuration file:
 
-### voms_user
+#### voms_user
 
 The Subject of the End-Entity certificate, used to sign the proxy.
 
 _Example_: ``/C=IT/O=IGI/CN=test0``
 
-### ssl_client_ee_s_dn
+#### ssl_client_ee_s_dn
 
 Like `voms_user`, the Subject of the End-Entity certificate. Unlike `voms_user`, it is available even for non-VOMS proxies and is formatted according to RFC 2253.
 
 _Example_: `CN=test0,O=IGI,C=IT`
 
-### voms_user_ca
+#### voms_user_ca
 
 The Issuer (Certificate Authority) of the End-Entity certificate.
 
 _Example_: `/C=IT/O=IGI/CN=Test CA`
 
-### ssl_client_ee_i_dn
+#### ssl_client_ee_i_dn
 
 Like `voms_user_ca`, the Issuer of the End-Entity certificate. Unlike `voms_user_ca`, it is available even for non-VOMS proxies and is formatted according to RFC 2253.
 
 _Example_: `CN=Test CA,O=IGI,C=IT`
 
-### voms_fqans
+#### voms_fqans
 
 A comma-separated list of Fully Qualified Attribute Names. See [The VOMS Attribute Certificate Format](http://ogf.org/documents/GFD.182.pdf) for more details.
 
 _Example_: `/test.vo/exp1,/test.vo/exp2,/test.vo/exp3/Role=PIPPO`
 
-### voms_server
+#### voms_server
 
 The Subject of the VOMS server certificate, used to sign the Attribute Certificate.
 
 _Example_: `/C=IT/O=IGI/CN=voms.example`
 
-### voms_server_ca
+#### voms_server_ca
 
 The Issuer (Certificate Authority) of the VOMS server certificate.
 
 _Example_: `/C=IT/O=IGI/CN=Test CA`
 
-### voms_vo
+#### voms_vo
 
 The name of the Virtual Organization (VO) to which the End Entity belongs.
 
 _Example_: `test.vo`
 
-### voms_server_uri
+#### voms_server_uri
 
 The hostname and port of the VOMS network service that issued the Attribute Certificate, in the form _hostname_ :_port_.
 
 _Example_: `voms.example:15000`
 
-### voms_not_before
+#### voms_not_before
 
 The date before which the Attribute Certificate is not yet valid, in the form _YYYYMMDDhhmmss_ `Z`.
 
 _Example_: `20180101000000Z`
 
-### voms_not_after
+#### voms_not_after
 
 The date after which the Attribute Certificate is not valid anymore, in the form _YYYYMMDDhhmmss_ `Z`.
 
 _Example_: `20180101120000Z`
 
-### voms_generic_attributes
+#### voms_generic_attributes
 
 A comma-separated list of attributes, each defined by three properties and formatted as `n=`_name_ `v=`_value_ `q=`_qualifier_. The qualifier typically coincides with the name of the VO.
 
 _Example_: `n=nickname v=newland q=test.vo,n=nickname v=giaco q=test.vo`
 
-### voms_serial
+#### voms_serial
 
 The serial number of the Attribute Certificate in hexadecimal format.
 
 _Example_: `7B`
 
+## Installation
+
+### prerequisites
+The module is written in C++, using features from C++14 that are supported by gcc v. 4.8.5 (the version available in CentOS 7) enabling the option `-std=c++1y` (see [`config.make`](config.make)). 
+
+The software dependecies are listed in the [provide-deps](docker/library-scripts/provide-deps.sh) script in the `docker` directory.
+
+The nginx source files are also needed. To download them in ```/tmp/nginx-x.y.z``` you can execute:
+
+```
+$ ngxVersion=<version>
+$ wget -O /tmp/nginx-$ngxVersion.tar.gz https://nginx.org/download/nginx-$ngxVersion.tar.gz
+$ cd /tmp && tar -xzvf /tmp/nginx-$ngxVersion.tar.gz && cd -
+```
+
+### Generic installation
+The generic installation instructions are:
+
+```shell
+$ cd /tmp/nginx-x.y.z
+$ ./configure --add-module=/path/to/ngx_http_voms_module
+$ make && make install
+```
+
+### Docker container
+
+A Docker image with nginx and the `ngx_http_voms_module` is available, you can find it [here](https://hub.docker.com/r/storm2/openresty-voms).
+
+### For the developers
+A [.devcontainer](.devcontainer) is provided for the developers with all the instructions on how to use it, how to build the rpm module and how to install it.
+
 ## Testing
 
-Setup and files to test the *ngx_http_voms_module* are contained in the [`t`](t) folder.
+Setup and files to test the `ngx_http_voms_module` are contained in the [`t`](t) folder.