Document some more features

Author: sam-mccall

README.md

@@ -65,12 +65,22 @@ index.
 
 Press `Ctrl-P #` to quickly navigate to a symbol by name.
 
+### Hover and inlay hints
+
+Clangd can describe almost any entity if you hover the mouse (or press Ctrl-KI).
+
+![Hover and inlay hints](doc-assets/hover.png)
+
+Inlay hints for parameters and deduced types can be shown temporarily or
+permanently (the `editor.inlayHints.enabled` setting controls this).
+
 ### Include management
 
 Code completion works across your codebase and adds `#include` directives where
 needed. The `•` shows includes that will be inserted.
 
-clangd can also suggest inserting missing #includes, where they cause errors.
+clangd can suggest inserting missing #includes, where they cause errors.
+It can [warn on unused includes](https://clangd.llvm.org/guides/include-cleaner).
 
 ![Fix inserts include](doc-assets/include.png)