Compatibility table: indicate recommended versions

[bowni]

The compatibility table becomes a pivotal information element for Substra users and enthusiasts, super useful.

1. However one might wonder which line he/she should consider. I suggest to add a subsection for indicating recommended versions (it will often be the last line, but maybe sometimes the previous one is more stable etc.).
2. For components which can be installed from sources and/or via Helm, it can be confusing to see two version numbers in the same cell of the table (hi @RomainGoussault 😄). It would super to clarify this (with an asterisk and footnote?)