Adds note about two approval policy to PR template (#10313)

* Adds note about two approval policy to PR template

* Adds qualifier to approval policy

Because, although two approvals is the general case, some PRs maybe merged with more or fewer approvals

[skip ci]

.github/PULL_REQUEST_TEMPLATE.md

@@ -2,6 +2,8 @@
 Before making a PR, please read our contributing guidelines
 https://github.com/babel/babel/blob/master/CONTRIBUTING.md
 
+Please note that the Babel Team requires two approvals before merging most PRs.
+
 For issue references: Add a comma-separated list of a [closing word](https://help.github.com/articles/closing-issues-via-commit-messages/) followed by the ticket number fixed by the PR. (it should be underlined in the preview if done correctly)
 
 If you are making a change that should have a docs update: submit another PR to https://github.com/babel/website