Update CONTRIBUTING.md

CONTRIBUTING.md

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 # Contributing to Erlang/OTP
 
+## License
+
+By making a contribution to this project, I certify that:
+(a) The contribution was created in whole or in part by me and I
+    have the right to submit it under the open source license
+    indicated in the file; or
+
+(b) The contribution is based upon previous work that, to the 
+    best of my knowledge, is covered under an appropriate open 
+    source license and I have the right under that license to   
+    submit that work with modifications, whether created in whole
+    or in part by me, under the same open source license (unless
+    I am permitted to submit under a different license), as 
+    Indicated in the file; or
+
+(c) The contribution was provided directly to me by some other
+    person who certified (a), (b) or (c) and I have not modified
+    it.
+
+(d) I understand and agree that this project and the contribution
+    are public and that a record of the contribution (including 
+    all personal information I submit with it, including my
+    sign-off) is maintained indefinitely and may be redistributed
+    consistent with this project or the open source license(s)
+    involved.
+
+Erlang/otp is licensed under the
+Apache License 2.0
+
+As stated in: LICENSE.txt 
+
+http://developercertificate.org/
+
 ## Reporting a bug
 
 Report bugs at https://bugs.erlang.org. See [Bug reports](https://github.com/erlang/otp/wiki/Bug-reports)