Fix bash completion path

The Bazel binary installer said
```
prefix="/usr/local"
bin="%prefix%/bin"
base="%prefix%/lib/bazel"
```
so the bash completion script should be in `/usr/local/lib/bazel/bin` when we run the installer as root.

Closes #8105.

PiperOrigin-RevId: 246816374

site/docs/completion.md

diff --git a/site/docs/completion.md b/site/docs/completion.md
index 1f6566d..89bb6ba 100644
--- a/site/docs/completion.md
+++ b/site/docs/completion.md
@@ -24,7 +24,7 @@
 
         Example: if you ran the installer with `--user`, this will be
         `$HOME/.bazel/bin`. If you ran the installer as root, this will be
-        `/usr/local/bazel/bin`.
+        `/usr/local/lib/bazel/bin`.
     2.  Do one of the following:
         *   Either copy this file to your completion directory (if you have
             one).