meson: Minimal README update

Acked-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Acked-by: Petri Latvala <petri.latvala@intel.com>
Acked-by: Daniel Stone <daniels@collabora.com>
Acked-by: Radoslaw Szwichtenberg <radoslaw.szwichtenberg@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/README b/README
index c3ddf76..2c2cd36 100644
--- a/README
+++ b/README
@@ -159,6 +159,22 @@
 	libasound2-dev
 	libgsl-dev
 
+Experimental meson build system support
+---------------------------------------
+
+Right now this is just a preview for developers, automake is still used by CI
+and needs to keep working. One-liner howto:
+
+$ mkdir build && meson build && cd build && ninja
+
+Note that meson insist on separate build directories from the source tree.
+
+Running testcases is done with
+
+$ cd build && ninja test
+
+gtkdocs is currently not yet supported.
+
 Releases for maintainers
 ------------------------