Providing guidance for MSRVs

[thejpster]

At the EWG meeting 2019-10-15, we discussed providing guidance on how to use MSRVs. This should probably be added to https://github.com/rust-embedded/wg/blob/master/ops/msrv.md.

The guidance should be around:

• What authors of HAL crates should do (the current guidance is only for EWG crates)
• How to check what your MSRV is
• Pointers to the docs (and hence current MSRV) of EWG architecture crates like cortex-m.
• Some key features (such as core::convert::Infallible) and their MSRV

Steps:

• Open a PR
• Get approval
• Merge the PR
• Profit

[MarcoIeni]

I don't know if this the right place to ask for this, but it would be nice to have guidance for MSRV in Github actions
here.
For example the 1.35.0 is only mentioned here and not in other parts of the document.

[BartMassey]

Closing this as part of 2024 triage. MSRV issues were resolved by #523.