[Misc] Rephrased to explain better the magical 5.6.6 version

README.md

@@ -78,7 +78,7 @@ docker run --net=xwiki-nw --name mysql-xwiki -v /my/own/mysql:/var/lib/mysql -e
 
 You should adapt the command line to use the passwords that you wish for the MySQL root password and for the xwiki user password.
 
-Note: If you're using MySQL < 5.6.6, you'll need to start MySQL with:
+Note: The `explicit-defaults-for-timestamp` parameter was introduced in MySQL 5.6.6 and will thus work only for that version and beyond. If you are using an older MySQL version, please use the following instead:
 
 ```console
 docker run --net=xwiki-nw --name mysql-xwiki -v /my/own/mysql:/var/lib/mysql -e MYSQL_ROOT_PASSWORD=xwiki -e MYSQL_USER=xwiki -e MYSQL_PASSWORD=xwiki -e MYSQL_DATABASE=xwiki -d mysql:5.7 --character-set-server=utf8 --collation-server=utf8_bin