Updated precompilers information in the Readme file

Ok, sorry for the delay, I had crazy weeks :). For clarity I reopened a new pull request.

Here is the pull request message :

I added precompilers information in the Readme file as you asked :). I added a list of supported extensions displayed as [jugglingdb adapters](https://github.com/1602/jugglingdb).

Let me know if something is not correct or missing :)