configure: Expand description of the LINKER_USE_RPATH setting

configure/CONFIG_SITE

@@ -183,7 +183,9 @@ EPICS_SITE_VERSION =
 # between the various stages of compilation.
 GCC_PIPE = NO
 
-#  Include RPATH when linking executables and libraries.
-#       must be either YES or NO
-LINKER_USE_RPATH=YES
+# Set RPATH when linking executables and libraries.
+#  Must be either YES or NO.  If you set this to NO you must also provide a
+#  way for Base executables to find their shared libraries when they are
+#  run at build-time, e.g. set the LD_LIBRARY_PATH environment variable.
+LINKER_USE_RPATH = YES