Link from js index

Author: aliu39

docs/platforms/javascript/common/feature-flags/index.mdx

@@ -34,4 +34,6 @@ Evaluation tracking requires enabling an SDK integration. Integrations are provi
 - [OpenFeature](/platforms/javascript/configuration/integrations/openfeature/)
 - [LaunchDarkly](/platforms/javascript/configuration/integrations/launchdarkly/)
 
+To manually track evaluations through an API, see the custom [FeatureFlags](/platforms/javascript/configuration/integrations/featureflags/) integration.
+
 <PlatformContent includePath="feature-flags/enable-change-tracking" />