update library README to include versions compatibility

[yangcao77]

Which area/kind this issue is related to?

/area library

Issue Description

Was initially pointed out by @kim-tsao:

I was thinking about having a section for version compatibility wrt to parent/plugin overriding or maybe documenting this as a limitation. Users may assume full interoperability otherwise.
devfile/library#125 (comment)

We need a section in the library README, for versions compatibility. including the parent/child version limit.(parent version cannot be greater than child version)
also should document some unsupported change from 2.0.0 -> 2.1.0 / 2.1.0 -> 2.2.0 which will be resulted into non-backward-compatible. i.e. plugin components, vscodeLaunch/vscodeTask commands , etc.

[thepetk]

closing as rotten (created > 2 years). Feel free to re-open if it's not a requirement.