Release process updates

[mbhealy]

Apologies for the delay, snow and family illness slowed things down.

Summary

As discussed at the 02/07/2024 TSC meeting this PR makes a few minor updates to the contributing guidelines to spell out what was decided regarding the release process.

In general we agreed to:

• Release when the TSC feels that this is warranted (e.g. based on the number or nature of changes accumulated)
• Spec changes that require backwards incompatible changes at the parsing level warrants a major version bump.
• Release v3.1 for the switch and other recent updates.

For the parser:

• The reference parser is an example implementation and not the true specification. It is used to vet proposed changes to the specification as a proof that they can be parsed and do not conflict egregiously with existing constructs.
• Regarding treatment of the OpenQASM version declaration in the parser:
  • It should generally be ignored by the reference parser for version-specific feature detection/support, but
  • Warnings for non-supported constructs in a specified version are appreciated but not required.
• The current list of versions supported by the parser will be listed within the parser itself. See Add supported_versions to openqasm3.spec. #513
• The parser is ready for a 1.0 release - supporting v3.1 of specification

TODO in upcoming PRs:

• Release notes need to be updated to separate parser and specification release notes
• Parser release notes need to be updated and cleaned up
• Spec version 3.1 needs to be tagged

[hodgestar]

What's here looks good to me.