update readme: add Learning resource

README.md

@@ -7,4 +7,10 @@ To understand  The software-defined networking well, I trying to create a simple
 ## TODOs
 
 - [ ] design structure of code and working.
-- [ ] write more description in README.
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+- [ ] write more description in README.
+
+## Learning resources
+
+[rust_ofp](https://github.com/baxtersa/rust_ofp)
+[awesome-sdn](https://github.com/sdnds-tw/awesome-sdn)
+[ryu](https://github.com/faucetsdn/ryu)
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