Update GOVERNANCE.md to list expectations of TSC members

In today's TSC meeting, we discussed a proposal to add text like the following to the GOVERNANCE.md document:

> TSC members are expected to help guide the Chapel project’s direction by…
…participating in TSC activities such as meetings, discussions, and votes
…seeking out and share opportunities to improve the project and grow the community over time
…being guided by what they consider to be best for the Chapel language, its users, the Chapel project, the historical investment in it, and its success going forward
…upholding Chapel’s [code of conduct](https://github.com/chapel-lang/chapel?tab=coc-ov-file) and being familiar with its [technical charter](https://github.com/chapel-lang/governance/blob/main/TechCharter.pdf)
…maintaining an LFX [openprofile.dev](https://openprofile.dev/) account for the sake of project voting and coordination

Based on feedback from @DanilaFe , here is a proposed minor update to the second item, discussed (maybe using slightly different words) during the meeting:

> …serving as an ambassador to the Chapel project, looking for ways to improve the project and grow the community over time

@ShreyasKhandekar suggested adding GitHub to the final bullet:

> …maintaining GitHub and LFX [openprofile.dev](https://openprofile.dev/) accounts for the sake of project voting and coordination

There seemed to be general consensus for all of the above, so this issue captures the TODO of making this addition to GOVERNANCE.md

Open GOVERNANCE.md and review the existing TSC member guidance and links. Add the agreed expectations, including participation, ambassadorship, project stewardship, Code of Conduct and Technical Charter familiarity, and GitHub and LFX Open Profile accounts. Done means the document clearly includes all five expectations and preserves the referenced links.

Written by the indexing model from the issue text.