Improve doc for `TEST_UNDECLARED_OUTPUTS_DIR`
As explained in commit
Closes
@@ -412,7 +412,10 @@ The initial environment block shall be composed as follows:
<tr>
<td><code>TEST_UNDECLARED_OUTPUTS_DIR</code></td>
<td>absolute path to a private writable directory (used to write undeclared
- test outputs)</td>
+ test outputs). Any files written to the
+ <code>TEST_UNDECLARED_OUTPUTS_DIR</code> directory will be zipped up and
+ added to an <code>outputs.zip</code> file under
+ <code>bazel-testlogs</code>.</td>
<td>optional</td>
</tr>
<tr>
