[clang-doc] Update clang-tools-extra release notes

clang-tools-extra/docs/ReleaseNotes.rst

@@ -144,6 +144,32 @@ Miscellaneous
 Improvements to clang-doc
 -------------------------
 
+- Use the Mustache HTML generator as the default HTML option.
+
+- Document concepts, typedefs, aliases, public class members, nested records, 
+  nested namespaces, global functions, global variables, protected methods and
+  members and friends in HTML.
+
+- Document ``throws`` comments in HTML.
+
+- Add definition location for classes in HTML.
+
+- Show class template declaration in HTML.
+
+- Add a top-level index page in HTML. This page lists the top-level namespaces
+  and serves as the documentation's root URL.
+
+- Add a ``Home`` button to the navigation bar which replaces non-useful buttons.
+  This new button links to the top-level index page.
+
+- Add a breadcrumb navigation bar to the navbar. This helps navigate through a
+  documented entity's context.
+
+- If a filename is too long, then the name will be truncated and the documented
+  entity's USR will be concatenated to guarantee its uniqueness.
+
+- Revert the flat directory structure to a nested directory structure.
+
 Improvements to clang-query
 ---------------------------