ref-manual/yocto-project-supported-features: add a contact for meta-arm

Set the contact address for meta-arm.

(From yocto-docs rev: 8ad91366ed89204affef6a72bd403b0d0a4525fa)

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/yocto-project-supported-features.rst

@@ -78,7 +78,7 @@ Below is a list of primary tested features, their maintainer(s) and builder(s):
      - meta-agl-core
    * - `meta-arm <https://git.yoctoproject.org/meta-arm>`__
      - meta-arm layer testing
-     - TBD
+     - meta-arm mailing list <meta-arm@lists.yoctoproject.org>
      - meta-arm
    * - `meta-aws <https://github.com/aws4embeddedlinux/meta-aws>`__
      - meta-aws layer testing