Update readme

Add note about supported yocto branches using markdown syntax, rename
the file to match.

Change-Id: Ic7e4a8d8a910ab75f1c43b05132ee22805b763ef
Reviewed-by: Mikko Gronoff <mikko.gronoff@qt.io>
Reviewed-by: Rami Potinkara <rami.potinkara@qt.io>

README

@@ -1,22 +0,0 @@
-Qt6 OpenEmbedded/Yocto Project layer
-====================================
-
-This layer depends on:
-
-URI: https://github.com/openembedded/openembedded-core (branch: master)
-
-Contributing
-------------
-
-To contribute to this layer you should submit the patches for review using
-Qt Gerrit (https://codereview.qt-project.org).
-
-More information about Qt Gerrit and how to use it:
-https://wiki.qt.io/Gerrit_Introduction
-https://wiki.qt.io/Setting_up_Gerrit
-
-Layer maintainers
------------------
-
-Samuli Piippo <samuli.piippo@qt.io>
-

README.md

@@ -0,0 +1,41 @@
+Qt6 OpenEmbedded/Yocto Project layer
+====================================
+
+This layer depends on:
+
+URI: https://github.com/openembedded/openembedded-core
+
+and optionally:
+
+URI: https://github.com/openembedded/meta-openembedded
+
+Yocto version support
+---------------------
+
+The branching of meta-qt6 layer follows Qt branching scheme, that is
+`dev` for the development branch, and `6.x` for each minor release.
+
+Following table shows the Yocto branches which are used to test each
+Qt version.
+
+| Yocto \ Qt | dev | 6.0 |
+| ---------- |:---:|:---:|
+| master     |  x  |  x  |
+| gatesgarth |  x  |  x  |
+| dunfell    |  x  |  x  |
+
+Contributing
+------------
+
+To contribute to this layer you should submit the patches for review using
+[Qt Gerrit](https://codereview.qt-project.org).
+
+More information about Qt Gerrit and how to use it:
+ - https://wiki.qt.io/Gerrit_Introduction
+ - https://wiki.qt.io/Setting_up_Gerrit
+
+Layer maintainers
+-----------------
+
+ - Samuli Piippo <samuli.piippo@qt.io>
+