docs: add qapi-domain syntax documentation

Who documents the documentation?

Me, I guess.

Signed-off-by: John Snow <[email protected]>
Message-ID: <[email protected]>
Acked-by: Markus Armbruster <[email protected]>
Signed-off-by: Markus Armbruster <[email protected]>

Author: jnsnow

docs/devel/index-build.rst

@@ -12,4 +12,5 @@ some of the basics if you are adding new files and targets to the build.
    kconfig
    docs
    qapi-code-gen
+   qapi-domain
    control-flow-integrity