Update the docs for the config file format.
Update the docs for the config file format.

* subversion/libsvn_subr/config_file.c (svn_config_ensure): Turn on the part
  of README.txt that talks about variable expansion, and note where the
  config files reside on Windows.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@845749 13f79535-47bb-0310-9956-ffa450edef68

wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion