[Scons-dev] README.rst edits

[Managan, Rob]

I made some edits to the README.rst that you can view at https://bitbucket.org/managan/scons_biblatex2.2

The changes are in the section on "Executing SCons Without Installing" about setting environment variables. 
I also note that after setting the SCONS_LIB_DIR environment variable I just run scons to get the local copy.

I think I have the format for setting environment variables according to your shell type right but I am no expert so I ask people check that. Mainly I want a Windows person to make sure this works on Windows. I did not know if just running scons will get the local copy after SCONS_LIB_DIR gets set.

Rob Managan