Issue #64: Update change log for removing bind() & undbind().

* Add summary in change log for removing the bind() and unbind()
functions.

Author: Gordon

affinity/cpp-20/d0796r3.md

@@ -16,6 +16,8 @@
 
 ### P0796r3 (SAN 2018)
 
+* Remove `this_thread::bind` & `this_thread::unbind` interface.s
+
 ### P0796r2 (RAP 2018)
 
 * Introduce a free function for retrieving the execution resource underlying the current thread of execution.