Update README.md
Update README.md

Specific add-on example (since the naming convention is slightly odd).
Add --all so the list includes deprecated/dependent packages.
Added tip about getting the correct add-on names.
Add instructions to install build_tools
Added support for extra's.
Merge remote-tracking branch 'ijansch/master'

Conflicts:
	README.md
Added support for extra's.
[blacksmith] Bump version
Add support for system-images
Merge pull request #19 from xadh00m/master

Add support for system-images
[blacksmith] Bump version
Fix directory name to check for system-images

Check for <android_sdk>/system-images/android-{system image version}
Merge pull request #20 from xadh00m/master

Fix directory name to check for system-images
[blacksmith] Bump version
Update gems
Issue #22 Fix typo
[blacksmith] Bump version
Add detect for ubuntu 14.04 and dont install ia32-libs
Add packages as described at http://bit.ly/1gI1nPl