Add info for the gm.py all-in-one script.
diff --git a/Building-with-GN.md b/Building-with-GN.md
index f0ded85..bdce11e 100644
--- a/Building-with-GN.md
+++ b/Building-with-GN.md
@@ -23,7 +23,18 @@
## Building
-There are two workflows for building V8. A raw workflow using commands on a lower level and a convenience workflow using wrapper scripts.
+There are two workflows for building V8. A raw workflow using commands on a lower level and a convenience workflow using wrapper scripts. There is also convenience all-in-one script that generates build files, triggers the build and optionally also runs the tests.
+
+#### Build instructions (all-in-one script)
+To use the helper script for instance for ```x64.release``` configuration, run:
+
+```tools/dev/gm.py x64.release```
+
+To run the tests right after the build, run:
+
+```tools/dev/gm.py x64.release.check```
+
+This helper script outputs all commands it's executing, so one can easily track them and re-execute if necessary.
#### Build instructions (convenience workflow)
