docs: Document Qt tools updates in 0.63

Especially relevant for users of Ubuntu 22.04 which has packages for
Qt 6.2 and Meson 0.61.

a606ce22e ("Add support for Qt 6.1+", 2022-01-08)
d68a0651e ("qt module: also prefer the changed name scheme for the tools", 2022-02-09)

docs/markdown/Qt6-module.md

@@ -2,9 +2,15 @@
 
 *New in Meson 0.57.0*
 
-The Qt6 module provides tools to automatically deal with the various
+The Qt6 module provides methods to automatically deal with the various
 tools and steps required for Qt.
 
+<div class="alert alert-warning">
+<strong>Warning:</strong> before version 0.63.0 Meson would fail to find
+Qt 6.1 or later due to the Qt tools having moved to the libexec subdirectory,
+and tool names being suffixed with only the Qt major version number e.g. qmake6.
+</div>
+
 ## compile_resources
 
 *New in 0.59.0*