Update user-manual.html

The double dash is in the wrong place in the example.

Closes bazelbuild#13532.

PiperOrigin-RevId: 378022925

site/docs/user-manual.html

@@ -2199,7 +2199,7 @@ <h2 id='run'>Running executables</h2>
   it is used to build <em>and run</em> a single target. Here is a typical session:
 </p>
 <pre>
-  % bazel run -- java/myapp:myapp --arg1 --arg2
+  % bazel run java/myapp:myapp -- --arg1 --arg2
   Welcome to Bazel
   INFO: Loading package: java/myapp
   INFO: Loading package: foo/bar