Add process doc for chairs to adopt proposal (#209)

* Add process doc for chairs to adopt proposal

Co-authored-by: Copilot <copilot@github.com>

* Consolidate repository setup steps in adoption process

Co-authored-by: Copilot <copilot@github.com>

* Clarify repository import process in adoption steps

Co-authored-by: Copilot <copilot@github.com>

---------

Co-authored-by: Copilot <copilot@github.com>

Author: liminzhu

README.md

@@ -4,6 +4,7 @@ This repo is for administration of the community group.
 
 - [Home page - wicg.io](https://wicg.io) - includes links to active incubations.
 - [Transferring a repo to WICG](https://github.com/WICG/admin/wiki/Process-to-transfer-a-repo)
+- [Adopting a proposal into WICG](adopting-a-proposal.md)
 - [Charter](https://wicg.github.io/admin/charter.html)
 - [Intent to migrate](intent-to-migrate.md)
 - [State of incubations](https://docs.google.com/spreadsheets/d/1K2EtkvKXMDk_h2goR34uMIWmw1LfPhIi-QAJHcQBP_4/edit?usp=sharing)

adopting-a-proposal.md

@@ -0,0 +1,30 @@
+## Adopting a proposal into WICG
+
+This document is process guidance for WICG chairs adopting proposals into WICG. Some operational links are only available to chairs and are intentionally omitted here.
+
+### Evaluate the proposal issue
+
+Review the proposal issue in the [WICG/proposals repository](https://github.com/WICG/proposals).
+
+The bar for adoption into WICG is intentionally low. A proposal is generally ready for adoption when there is active discussion or a single point of interest in the issue, and the proposal is not yet a better fit for another Community Group or Working Group.
+
+When assessing interest, generally do not count support from people at the same company as the proposal author.
+
+### Coordinate with the proposal owner
+
+Once a proposal is ready for adoption, a chair should contact the proposal owner and work with them to move the proposal into a dedicated repository under the WICG organization.
+
+There are three common ways to do this. Use judgment based on the current repository setup and the relationship between the author and the chair.
+
+1. If a chair already has admin access to an existing proposal repository, the chair can transfer that repository directly into WICG. This can happen when the chair and the author work at the same company.
+2. The author can transfer an existing proposal repository to a chair, and the chair can then transfer it into the WICG organization.
+3. A chair can create a new repository under WICG and grant the proposal author maintainer access so that the author can push the proposal content there.
+
+### Complete the adoption steps
+
+After the repository is established under WICG, the chair handling the adoption should complete the remaining follow-up work.
+
+1. Notify the participants on the original issue in [WICG/proposals](https://github.com/WICG/proposals) and close that issue.
+2. Add the proposal to the WICG tracking sheet shared among chairs.
+3. Import the repository using W3C Repository Manager (link in the tracking sheet), and make sure the repository includes and configures `w3c.json`, `CONTRIBUTING.md`, `LICENSE.md`, and `CODE_OF_CONDUCT.md`.
+4. Announce the new repository on public-new-work@w3.org.