Added documentation for some options

I had to look around source a little bit to find how to tweak the admin the way I want it to behave.
The options are there, it's a pity they aren't documented, so here's my try at it.
I didn't document model.formage.form and model.formage.post because I'm not sure yet how it works...
Example more in line with the 'song' model
Fix missing single-quote
Merge pull request #12 from LaurentVB/patch-1

Documentation of options in README