Fix cygwin not able to process 'configure' when fetched on windows directly.
* Edited README.txt with GIT installation instructions. Signed-off-by: Euphy <euphy@rathena.org> git-svn-id: https://svn.code.sf.net/p/rathena/svn/trunk@17421 54d463be-8e91-2dee-dedb-b68131a5f0ec