chore(clangd): change filetypes and notes on how to get it to recognize some local headers

README.md

@@ -36,6 +36,11 @@ unless you add a `.luarc.json` file with the following content:
 }
 ```
 
+### Clangd
+If `clangd` can't find some headers, then you need to create a `compile_commands.json` file.
+When a `Makefile` is present (or other build tools such as `cmake` are used, look up how to do that online), you can use `bear` as follows to create this file:
+`bear -- make`. That's it
+
 ### Java
 #### jdtls
 Ensure you have jdk21-opnejdk or newer installed. On Arch (and derivatives) you can switch the preferred java version using `archlinux-java set <version name>`