local.conf.sample: Add commented out OPENHARMONY_VERSION definition

Signed-off-by: Thierry Escande <thierry.escande@huawei.com>

conf/local.conf.sample

@@ -106,3 +106,11 @@ RM_WORK_EXCLUDE += "qemu-helper-native"
 # Use out-of-China mirror of OpenHarmony git repositories.
 #
 MIRRORS:prepend = "git://gitee.com/openharmony/ git://github.com/openharmony/ \n "
+
+#
+# Choose OpenHarmony version
+#
+# Uncomment to overwrite the variable OPENHARMONY_VERSION set in the
+# distro configuration file.
+#
+#OPENHARMONY_VERSION = "3.0"