DOC: prerequisites unclear

[keithbriggs]

README.md says:

The current master/head version requires either of
OMNeT++ 5.5.1 and INET 3.6.6

The word "either" implies two alternatives. But we never say "either ... and", only "either ... or".

Then INSTALL.md says

You should have a
working OMNeT++ (v5.5.1) installation. (Download from http://omnetpp.org)
working INET-Framework installation (v3.6.6). (Download from http://inet.omnetpp.org)

which implies that both are needed.

The wording in both these should be cleaned up to say precisely what is required. is it either or both?