Add FB number in the comment

src/objective-c/README-CFSTREAM.md

@@ -24,14 +24,14 @@ case of problem and you want to disable CFStream on iOS, you can set environment
 "grpc\_cfstream=0".
 
 ## Caveats
-It is known to us that the CFStream API has some bug which will cause gRPC's CFStream networking
+It is known to us that the CFStream API has some bug (FB6162039) which will cause gRPC's CFStream
-layer to stall occasionally. The issue mostly occur on MacOS systems (including iOS simulators on
+networking layer to stall occasionally. The issue mostly occur on MacOS systems (including iOS
-MacOS); iOS may be affected too but we have not seen issue there. gRPC provides a workaround to this
+simulators on MacOS); iOS may be affected too but we have not seen issue there. gRPC provides a
-problem with an alternative poller based on CFRunLoop. The poller can be enabled by setting
+workaround to this problem with an alternative poller based on CFRunLoop. The poller can be enabled
-environment variable `GRPC_CFSTREAM_RUN_LOOP=1`. Note that the poller is a client side only poller
+by setting environment variable `GRPC_CFSTREAM_RUN_LOOP=1`. Note that the poller is a client side
-that does not support running a server on it. That means if an app opts in to the CFRunLoop-based
+only poller that does not support running a server on it. That means if an app opts in to the
-poller, the app cannot host a gRPC server (gRPC Objective-C does not support running a server but
+CFRunLoop-based poller, the app cannot host a gRPC server (gRPC Objective-C does not support running
-other languages running on iOS do support it).
+a server but other languages running on iOS do support it).
 
 ## Notes