docs: Third-party patent disclosure

Author: kmeisthax

README.md

@@ -48,6 +48,14 @@ at your option.
 
 h263-rs depends on third-party libraries under compatible licenses. See [LICENSE.md](LICENSE.md) for full information.
 
+### Third-party patents
+
+The ITU-T H.263 standard, it's Annexes, and various nonstandard extensions to them, potentially contain inventions that are claimed by one or more third-party patents outside the scope of the Apache License's patent grant. We do not and can not warranty or indemnify users of `h263-rs` against such third-party claims.
+
+It is the belief of Ruffle's maintainers that the default feature configuration of `h263-rs` contains only inventions whose patents have either expired in the United States, or are licensed under "Option 1" terms (as defined in [ITU-T Common Patent Policy](https://www.itu.int/en/ITU-T/ipr/Pages/policy.aspx) Section 2.1). Specifically, we have no knowledge of a standards-essential patent covering H.263 alone or the Sorensen Spark flavor of H.263.
+
+At times, certain features of the library may come under patent claims licensed under "Option 2" or "Option 3" terms (as defined in [ITU-T Common Patent Policy](https://www.itu.int/en/ITU-T/ipr/Pages/policy.aspx) Section 2.2 and 2.3). This can happen if we implement additional patented annexes of H.263, or if unknown patent claims (commonly known as "submarine patents") are brought to our attention. When this happens, we will update the library so that the encumbered code is excluded from the default configuration, and add a new Cargo feature named after the patent claiming the invention. Those who have licensed the patent may then enable such patented functionality. If you have knowledge of such a patent, please [file an issue about it](https://github.com/ruffle-rs/h263-rs/issues/new/choose).
+
 ### Contribution
 
 h263-rs welcomes contribution from everyone. See [CONTRIBUTING.md](CONTRIBUTING.md) for help getting started.