Add linting instructions to AGENTS.md

This prevents the agent from "fixing" lint errors by writing #[allow]
indiscrimintantly.

Change-Id: I1161dcbe90ae73f02d75c2462fc6fe136a6a6964
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/23600
Commit-Queue: Matt Stark <msta@google.com>
Reviewed-by: Takuto Ikuta <tikuta@google.com>

.agents/AGENTS.md

diff --git a/.agents/AGENTS.md b/.agents/AGENTS.md
index 478fcfe..350d431 100644
--- a/.agents/AGENTS.md
+++ b/.agents/AGENTS.md
@@ -25,6 +25,11 @@
   `// Safety: <reason>` comment explaining why the usage is safe.
 * **Warnings**: The code (including the tests) should compile with no warnings
   and no clippy lint errors.
+* If you ever believe that #[allow] is required to bypass the linter:
+  * You *must* get permission from the user.
+  * You *must* write a comment above the allow saying why we need it.
+  * You *must* put it in as specific a place as is feasible. Avoid, for
+    example, allowing a lint for a whole file.
 
 ## Imports & Use Statements