document reqd. approvals for target changes

Author: davidtwco

src/compiler/proposals-and-stabilization.md

@@ -263,11 +263,20 @@ circumstance.
     in the description
   - New targets should be assigned to the compiler team co-leads to ensure that any demands on
     the project infrastructure are considered and checked with relevant teams
+- Renaming a target or making a breaking change to a target
+  - **Propose using:** PR
+  - **Approve using:** FCP
+  - Open a PR with the new changes and describe the motivation for the change. Once reviewed,
+    start an FCP.
+  - If this affects a tier two or tier one target, it should be accompanied by a blog post
+    announcing the change and a notice period before the change applies.
 - Demoting/removing a target
   - **Propose using:** MCP
   - **Approve using:** FCP
   - Write an MCP describing why the target should be demoted/removed and once discussion has
     concluded, an FCP can be started to approve the demotion/removal.
+  - If this affects a tier two or tier one target, it should be accompanied by a blog post
+    announcing the change and a notice period before the change applies.
 - Changing target baseline (e.g. minimum Darwin or Windows version bump)
   - **Propose using:** MCP
   - **Approve using:** FCP