Add standard IETF license. Fixes #11. (#20)

LICENSE.md

@@ -0,0 +1,19 @@
+# License
+
+This repository relates to activities in the [Internet Engineering Task
+Force (IETF)](https://www.ietf.org/). All material in this repository is
+considered Contributions to the IETF Standards Process, as defined in
+the intellectual property policies of the IETF currently designated as
+[BCP 78](https://www.rfc-editor.org/info/bcp78),
+[BCP 79](https://www.rfc-editor.org/info/bcp79) and the [IETF Trust
+Legal Provisions (TLP) Relating to IETF
+Documents](https://trustee.ietf.org/trust-legal-provisions.html).
+
+Any edit, commit, pull request, issue, comment or other change made to
+this repository constitutes Contributions to the [IETF Standards
+Process](https://www.rfc-editor.org/info/bcp9).
+
+You agree to comply with all applicable IETF policies and procedures,
+including, BCP 78, 79, the TLP, and the TLP rules regarding code
+components (e.g., being subject to a Revised BSD License) in
+Contributions.