Add editor for GNU/Linux

AFAIK textedit isn't include in all GNU/Linux distribution.
I add gedit as the GNU/Linux text editor.

I change the order of the configure commands to be the same of
present in the text.
Improves base on comments about editor for git

I set GNU nano as the recommended editor and change the position
of some information to not duplicate it.
Some changes about editor for git

Make changes suggest by @ahmadia.
Grammar fix in swc-git

Thanks to @ahmadia.
Merge pull request #52 from r-gaia-cs/git-editor

Add editor for GNU/Linux in swc-git