Readme - remove wrong explanation of the FDL.

It was correct for the CC-SA license, but the FDL has more caveats, which need
more explaining. I'm not willing to do that right now, so I've instead switched
the "read the license" explanation. It's not actually that hard to read, I
recommend reading it.
Ch 1 - remove incorrect explanation of FDL.

The explanation is now "read the license".
Merge branch 'f-fdlfix' into develop