Getting commit access (#4246)

Establish a process for getting commit access. We will:

-   Grant access based on a developer's commit history.
- Someone with commit access should nominate, and a contributor may ask.
    -   A lead will approve nominations. Only one lead is needed.
-   Remove commit access once someone is idle for 6 months.
- "Idle" means no significant project activity on any of GitHub,
Discord,
        or in meetings.
    -   Access removed due to being idle will be restored on request.

---------

Co-authored-by: Chandler Carruth <chandlerc@gmail.com>

docs/project/commit_access.md

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+# Commit access
+
+<!--
+Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+Exceptions. See /LICENSE for license information.
+SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+-->
+
+<!-- toc -->
+
+## Table of contents
+
+-   [Overview](#overview)
+-   [Getting access](#getting-access)
+-   [Removing access](#removing-access)
+
+<!-- tocstop -->
+
+## Overview
+
+First and foremost, commit access is **not required** for contributing to
+Carbon! Anyone can send a pull request with a change to Carbon. Very few parts
+of our process require commit access, and most development activity is exactly
+the same for folks with or without. This is an important feature of our GitHub
+workflow for us, and one we plan to keep.
+
+The main thing commit access allows is for developers to merge PRs into the main
+[carbon-lang repository](https://github.com/carbon-language/carbon-lang/). They
+still need review, and often a reviewer with commit access handles the merge. It
+also gives the ability to [approve and merge changes](code_review.md).
+
+Getting commit access can help ease the development process; for contributors
+who don't feel comfortable doing reviews, it can still ease the review process
+for their own PRs. It allows authors to automatically get GitHub Action results
+and merge their own PRs, including after resolving conflicts or fixing trivial
+PR comments post-approval.
+
+Developers with commit access are expected to make reasonable choices about when
+to approve or merge PRs for others. Generally, the change either needs to be
+trivially understood without context on the code in question (such as a cleanup
+or typo fix), or the developer should have some context on the code in question.
+If in doubt, feel free to review but leave approving or merging for someone
+else.
+
+Similarly, developers with commit access are expected to make reasonable choices
+about what changes to make to their own PRs without asking for another round of
+review prior to merge, even after approval. And again, if in doubt, ask for
+review.
+
+## Getting access
+
+Contributors can request commit access based on their commit history. We want to
+make sure that developers with commit access are reasonably familiar with the
+style and structure of the codebase. Access will typically be granted when
+developers have contributed several PRs and are expecting to continue making
+more.
+
+After a few non-trivial PRs are merged, contributors can ask a reviewer to
+nominate them for commit access if they plan to keep contributing. Reviewers can
+also directly suggest and nominate someone. Nominations need to be approved by
+at least one lead.
+
+When approved, an invitation will be sent to join the
+[Commit access team](https://github.com/orgs/carbon-language/teams/commit-access)
+on GitHub. The invitation should cause a notification from GitHub, but it's also
+possible to go to the
+[invitation link](https://github.com/orgs/carbon-language/invitation) directly.
+Access is granted when the invitation is accepted.
+
+## Removing access
+
+We'll periodically remove commit access from contributors who have been idle for
+over 6 months. We'll use a combination of sources to determine what "idle"
+means, including whether a developer has been either sending or reviewing PRs.
+Developers can ask for commit access to be restored if they plan to start
+contributing again or come back from a break. Any relevant past contributions
+will still apply and allow it to be restored trivially.
+
+For example, for `jonmeow`, GitHub searches (defaulting to PRs for convenience,
+but other types are included):
+
+-   [repository:carbon-language/carbon-lang author:jonmeow](https://github.com/search?q=repository%3Acarbon-language%2Fcarbon-lang+author%3Ajonmeow&type=pullrequests)
+-   [repository:carbon-language/carbon-lang commenter:jonmeow](https://github.com/search?q=repository%3Acarbon-language%2Fcarbon-lang+commenter%3Ajonmeow&type=pullrequests)