Improve the warning message

README.md

@@ -1,4 +1,6 @@
-<aside class="warning">
+ :warning: Warning
+==================
+
 **Be very careful when using `master`**, especially if you are currently running
 `1.4`, development of version `1.5` includes refactoring the frontend and
 authentication mechanisms. At best your server will stop working, at worst you
@@ -8,7 +10,6 @@ could expose your data to malicious attackers!
 to replace nginx because certificate generation was a nightmare. As we are in the
 process of completely rewriting the frontend and authentication interface, it will
 probably be deprecated before `1.5` is out.
-</aside>
 
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