Clarify distinction between README and README.md

[fingolfin]

It's not clear to me why there are both a README and a README.md file. Perhaps the intention is to merge the two? Then this should be recorded somewhere (e.g. this issue ;-).

Or perhaps they are meant to stay in parallel, which is also fine. But then I'd point from README.md to README. And I'd consider renaming README to e.g. NOTES or INTERNALS or whatever (and perhaps also convert it to Markdown?)

[olexandr-konovalov]

README is the old file by the initial authors. README.md new, created when work on the package was started. Agree that this requires some revision!

[fingolfin]

From the looks of it, I think a big part of README should actually be put into the package manual. The rest can be merged into README.md