Document release shard timeout limitation

Change-Id: I57d0e24924fb5ec649be6e62f755334584fe7c65
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/63960
Reviewed-by: Victoria Ashworth <vashworth@google.com>
Commit-Queue: Reid Baker <reidbaker@google.com>
diff --git a/recipe_modules/shard_util/api.py b/recipe_modules/shard_util/api.py
index 257fc9d..a702308 100644
--- a/recipe_modules/shard_util/api.py
+++ b/recipe_modules/shard_util/api.py
@@ -395,6 +395,10 @@
       timeout_in_minutes = build.get('timeout', None)
 
       if self.m.common.is_release_candidate_branch(branch):
+        # `timout_in_minutes` only applys to the shard being run
+        # not the task launching the shard. That means for practical
+        # reasons timeout should be less than the timeout value in
+        # go/flutter-internal-release-release-builder
         # Due to limited capacity for release builds, extend timeout
         timeout_in_minutes = max(
             timeout_in_minutes if timeout_in_minutes is not None else 0,