add gitignore to not to download into machine code example

Example 1: how to put files into gitignore

$ echo debug.log >> .gitignore
$ git rm --cached debug.log
rm 'debug.log'
$ git commit -m "Start ignoring debug.log"

Example 2: git ignore content of a folder

# exclude everything
somefolder/*

# exception to the rule
!somefolder/.gitkeep