Stronger and more specific warning.

doc/install/installation.md

@@ -156,7 +156,7 @@ To setup the MySQL/PostgreSQL database and dependencies please see [`doc/install
     sudo -u git -H git checkout 5-3-stable
 **Note:**
-You can change `5-3-stable` to `master` if you want the *bleeding edge* version, but do so with caution!
+You can change `5-3-stable` to `master` if you want the *bleeding edge* version, but never install master on a production server!
 ## Configure it