Update README.md

Author: wu-sheng

README.md

@@ -1 +1,12 @@
-# java-plugin-extensions
+# SkyWalking javaagent plugin extensions
+Due to license incompatibilities/restrictions, some plugins are hosted in here.
+
+Including
+1. Resin 3
+1. Resin 4
+1. Oracle JDBC Driver
+
+To be clear, these plugins have no license issue, but need Apache 2.0 uncompatible license Jar file to compile, which is not allowed to do in Apache. 
+
+# License
+Apache 2.0