Create pull request template for new charters for easier voting

Background or context to help others understand the change.

When I made this pull request to initiate a vote on the new charter for the DEI committee, it seemed like there wasn't a very well-established way to make a vote. I had to go through the Jupyter about page and manually copy / paste the github handles and names of EC / SSC members. I also wasn't sure that it was the correct way to initiate a vote.

A brief summary of the change.

This adds a template for pull requests so that anyone trying to create a new working group / standing committee will have an easier time initiating a vote (and can focus on the important stuff that they're working on for the committee!).

What is the reason for this change?

Helps encourage people to make new working groups / standing committees by making the process easier and more well defined.
Saves people time by not needing to copy and paste a bunch of github handles / names

Alternatives to making this change and other considerations.

We could move to another type of voting! But if this is how we're voting, I think it makes sense for there to be a template.

jupyter / governance