Decide on appropriate abstain emoji; add to contribution guide

[aaraney]

@cmbarton clarified during the 12/6/2021 meeting that there are three voting states: yes, no, or abstain. In the 'How to Vote on a Pull Request' section of the contribution guide there are only two options 👍 or 👎. Can we decide and add an abstain emoji?

[aaraney]

My proposal is 😕.

[alee]

I like 😕 but 👀 might work too

[aaraney]

Hahah, I really like 👀. I think you've converted me.

[cmbarton]

After this meeting, I think we will need to have a more well defined method of voting. We an pick our own emoji's for abstain like this 🤷 U+1F937 SHRUG, decimal: 129335, HTML: &#129335