Readme updates.
diff --git a/COPYING b/COPYING
index d774506..3167a00 100644
--- a/COPYING
+++ b/COPYING
@@ -30,3 +30,15 @@
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+Opus is subject to the royalty-free patent licenses which are
+specified at:
+
+Xiph.Org Foundation:
+https://datatracker.ietf.org/ipr/1524/
+
+Skype Limited:
+https://datatracker.ietf.org/ipr/1602/
+
+Broadcom Corporation:
+https://datatracker.ietf.org/ipr/1526/