DOCS: Clarification of "compilation_mode" as "-c"

RELNOTES: None
PiperOrigin-RevId: 320535377
diff --git a/site/docs/user-manual.html b/site/docs/user-manual.html
index 33ac7bd..67cb82e 100644
--- a/site/docs/user-manual.html
+++ b/site/docs/user-manual.html
@@ -456,7 +456,8 @@
 
 <h4 id='flag--compilation_mode'><code class='flag'>--compilation_mode (fastbuild|opt|dbg)</code> (-c)</h4>
 <p>
-  This option takes an argument of <code>fastbuild</code>, <code>dbg</code>
+  The <code class="flag">--compilation_mode</code> option (often shortened to <code>-c</code>,
+  especially <code>-c opt</code>) takes an argument of <code>fastbuild</code>, <code>dbg</code>
   or <code>opt</code>, and affects various C/C++ code-generation
   options, such as the level of optimization and the completeness of
   debug tables.  Bazel uses a different output directory for each