RFC 127: Add RFC Exemption for testdriver.js methods similar to WebDriver endpoints

rfcs/rfc_exemption_testdriver_method.md

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+# RFC 127: Add RFC Exemption for testdriver.js methods similar to WebDriver endpoints
+
+## Summary
+
+To expedite changes and reduce developer friction, the web-platform-tests
+community should consider allowing a developer to bypass the RFC process if the
+developer is only extending testdriver.js with a method similar to an existing
+WebDriver endpoint.
+
+## Details
+
+During the 2022-10-04 [meeting](https://github.com/web-platform-tests/wpt-notes/blob/master/minutes/2022-10-04.md),
+attendees discussed RFC [#121](https://github.com/web-platform-tests/rfcs/pull/121)
+and similar changes to testdriver.js. Attendees decided that RFC 121 could land
+automatically if the WebDriver changes landed first.
+
+Scaling the learnings from that, this RFC proposes that the README should add a
+RFC exemption for `extending testdriver.js with a method that closely matches a WebDriver endpoint`.
+
+To make the reviewer aware of the type of change, PR author should add the
+`testdriver.js` label to the PR.
+
+## Risks
+
+Low/minimal risks:
+- A developer trying to extend testdriver.js with a method that does not match
+  an existing WebDriver endpoint.
+  - Mitigation:
+    - The PR review process can catch this if the WebDriver endpoint already
+      exists.