ref-system-requirements.rst: Add Fedora 33 and 34 to list of supported distros

(From yocto-docs rev: b85b532b8360756798c08482b94758d5df55f5ed)

Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/system-requirements.rst

@@ -49,6 +49,10 @@ distributions:
 
 -  Fedora 32
 
+-  Fedora 33
+
+-  Fedora 34
+
 -  CentOS 7.x
 
 -  CentOS 8.x