Quick fix of"HOME_DIR" variable and small improvement of Readme

Created by: mr-kenhoff

Hello,

the variable HOME_DIR should point to the current users home folder in the msys environment. When multiple user folders existed, the HOME_DIR variable incorrectly contained a list of all users, not just the one logged in. That caused the build to fail. I fixed that by explicitly setting the variable depending on the currently logged in windows user.

Furthermore I made some minor tweaks to the Readme. In the next few days I wanted to extend the Readme a little more in the hope that it will be usefull for new users.