Add policy for determining Project Director substitutes

[rylev]

This solves an ambiguity about what to do when a Project Director cannot make a Foundation Board meeting. Instead of there being UB where in practice the PD in question decided on their own, this document lies out a simple procedure for choosing a sub.

Supersedes #61

@ehuss can you kick off the review process again and check off those who have already given their checkmark?

[ehuss]

@rfcbot fcp merge

I'm going to check boxes from https://github.com/rust-lang/leadership-council/pull/61#issuecomment-1897739373, assuming everyone is fine with the minor updates that have been made.

[rfcbot]

Team member @ehuss has proposed to merge this. The next step is review by the rest of the tagged team members:

• [x] @Mark-Simulacrum
• [ ] @carols10cents
• [x] @eholk
• [x] @ehuss
• [x] @jackh726
• [x] @jonathanpallant
• [x] @m-ou-se
• [x] @technetos

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[rfcbot]

:bell: This is now entering its final comment period, as per the review above. :bell:

[rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.