Document --action_env in the user manual.
Fixes
RELNOTES:
@@ -491,6 +491,18 @@ the compilation of binaries during the build.
used CROSSTOOL file.
</p>
+<h4 id='flag--action_env'>
+ <code class='flag'>--action_env=<var>VAR=VALUE</var></code>
+</h4>
+<p>
+ Specifies the set of environment variables available during the execution of all actions.
+ Variables can be either specified by name, in which case the value will be taken from the
+ invocation environment, or by the `name=value` pair which sets the value independent of the
+ invocation environment.
+
+ This `--action_env` flag can be specified multiple times. If a value is assigned to the same
+ variable across multiple `--action_env` flags, the latest assignment wins.
+</p>
<h4 id='flag--experimental_action_listener'>
<code class='flag'>--experimental_action_listener=<var>label</var></code>
