Add installation guide to Readme file
Remove tab from empty line.

If editing and saving Arduino.mk with emacs, emacs complains about
"Suspicious line 1050". This line is empty but contains an extra tab.

Signed-off-by: Ralf Doering <ralf@rdoering.net>
Merge pull request #89 from ralfdoering/fix-whitespace-revised

Remove tab from empty line.