Added zsh autocomplete hint for compdump reinit 

Change-Id: Idd5bb62371be8ba5c02f3d5352ce9577251049d0

Closes #2340.

--
Change-Id: Idd5bb62371be8ba5c02f3d5352ce9577251049d0
Reviewed-on: https://github.com/bazelbuild/bazel/pull/2340
PiperOrigin-RevId: 145395969
MOS_MIGRATED_REVID=145395969
diff --git a/site/versions/master/docs/install.md b/site/versions/master/docs/install.md
index fe4194d..0a6f9e5 100644
--- a/site/versions/master/docs/install.md
+++ b/site/versions/master/docs/install.md
@@ -311,6 +311,9 @@
     cp scripts/zsh_completion/_bazel ~/.zsh/completion
     ```
 
+    You may have to call `rm -f ~/.zcompdump; compinit`
+    the first time to make it work.
+
 2. Optionally, add the following to your .zshrc.
 
     ```