add doc for new `Skip-Clang-Tidy-Checks` footer

Bug: 388321980
Change-Id: Id40d5c5a16bedfbe316cccc4e6c285be2c0aafa7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6176007
Reviewed-by: Ben Pastene <[email protected]>
Reviewed-by: Garrett Beaty <[email protected]>
Auto-Submit: Yiwei Zhang <[email protected]>
Commit-Queue: Garrett Beaty <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1406794}
diff --git a/docs/infra/cq.md b/docs/infra/cq.md
index a61b18c..eee83fa 100644
--- a/docs/infra/cq.md
+++ b/docs/infra/cq.md
@@ -136,6 +136,17 @@
   This will disable the `test new tests for flakiness.*` steps in CQ builds that
   check new tests for flakiness.
 
+* `Skip-Clang-Tidy-Checks: <check_1>,<check_2>,...`
+
+  This will skip the specified clang-tidy checks. The checks can be specified
+  as check name (e.g. `modernize-use-equals-default`) or glob to skip a set of
+  checks (e.g. `modernize-*` to skip checks that advocate usage of modern
+  language constructs). This option can span across multiple lines, for example:
+  ```
+  Skip-Clang-Tidy-Checks: google-explicit-constructor
+  Skip-Clang-Tidy-Checks: modernize-*,readability-*
+  ```
+
 ## FAQ
 
 ### What exactly does the CQ run?