Installation instructions are outdated

Note: I only read the "Unix-like Installation". Since the last release is from 2012, so no fresh tarball to download, so I would change the instructions in readme:

- git clone repo (git clone https://github.com/codebrainz/geany-themes.git) or download as zip (https://github.com/codebrainz/geany-themes/archive/master.zip) and extract it
- change to the root directory of the project, and execute 'make install'
- go to geany (no restart seems to be required) and chose your color scheme:
"View" -> "Change Color Scheme..."
(BTW this is not obvious, so better to document, I first searched it in Preferences)