Add to readme info about versions of stack used

[crtahlin]

Add a section to readme, with info about which versions are used, e.g.:

Stack versions

master : bee 1.8.0; FairOS 1.0.1; blockchain 2.2.2
release 0.1 : bee 1.7.9; FairOS 1.0.0, blockain 2.2.2
...

Something like that. The idea behind this is, that dev should know which combination of versions they are working on, to be sure they can deploy to (same) mainnet.