Replace README with README.md

[mvidner]

Continuing the series from #9.

It is not intended to be merged but

• to continue a discussion about how YaST module README.md files should generally look like
• to give @jreidinger a template to base yast2-installation/README.md on ;-)

[jreidinger]

I miss here links to possible developer documentation living in module like own agent or some design document. Where it should go?

[mvidner]

I added (linked) it above in the Documentation section.

[mvidner]

OK, so the remaining things for this one are

• replace A B C with the actual features
• make a section/link for module-specific developer documentation (there is some outdated docs, but removing it is out of scope here)

I will do it this week

[mvidner]

I hope this is finally ready for merge, after a long delay on my part. @dmajda @jreidinger OK?

[jreidinger]

Looks good to me