[build] Fix lenient_api_summary docs

Change-Id: I3be2cb383b07f1da11ca818e105cb9350857bc85
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/693808
Commit-Queue: Auto-Submit <auto-submit@fuchsia-infra.iam.gserviceaccount.com>
Fuchsia-Auto-Submit: Kendal Harland <kjharland@google.com>
Reviewed-by: Alex Zaslavsky <azaslavsky@google.com>
diff --git a/build/fidl/fidl.gni b/build/fidl/fidl.gni
index 7b92e82..0b26889 100644
--- a/build/fidl/fidl.gni
+++ b/build/fidl/fidl.gni
@@ -73,10 +73,10 @@
 #     If set to false, the linting step is skipped.
 #
 #   lenient_api_summary (optional, boolean, default false)
-#     If set, the builder will check the generated FIDL API summary files against
-#     their checked in version.  If unset, or false, no such check will happen.
-#     This switch is used to deploy API summary checks across petals without
-#     breaking global integration. See fxb/68951 for details.
+#     If false, the builder will check the generated FIDL API summary files against
+#     their checked in version.  If true, the checks will emit warnings instead
+#     of errors. This switch is used to deploy API summary checks across petals
+#     without breaking global integration.
 #
 #   dart_analysis (optional, boolean, default false)
 #     If set to true, dart analysis is run on generated Dart bindings.