Update extensions README

extensions/README.md

@@ -1,15 +1,3 @@
-== FreshRSS extensions ==
+# FreshRSS extensions
 
 You may place in this directory some custom extensions for FreshRSS.
-
-The structure must be:
-
-./FreshRSS/extensions/
-	./NameOfExtensionAlphanumeric/
-		./style.css
-		./script.js
-		./module.php
-
-Each file is optional.
-
-The name of non-official extensions should start by an 'x'.