Add --noblock_for_lock exit code to documentation

The source for this is https://github.com/bazelbuild/bazel/blob/ac48e65f702d3e135bb0b6729392f9cb485da100/src/main/cpp/util/exit_code.h#L35-L37

Closes #14871.

PiperOrigin-RevId: 431517053
diff --git a/site/en/docs/scripts.md b/site/en/docs/scripts.md
index bd21f77..d324b40 100644
--- a/site/en/docs/scripts.md
+++ b/site/en/docs/scripts.md
@@ -46,6 +46,7 @@
 -   `2` - Command Line Problem, Bad or Illegal flags or command combination, or
     Bad Environment Variables. Your command line must be modified.
 -   `8` - Build Interrupted but we terminated with an orderly shutdown.
+-   `9` - The server lock is held and `--noblock_for_lock` was passed.
 -   `32` - External Environment Failure not on this machine.
 
 -   `33` - Bazel ran out of memory and crashed. You need to modify your command line.