gnomeExtensions: improve README

Document that the all-packages.nix needs to be updated too (this was forgotten
in the GNOME 41 update). Also fixed typos.

pkgs/desktops/gnome/extensions/README.md

@@ -4,7 +4,7 @@ All extensions are packaged automatically. They can be found in the `pkgs.gnomeX
 
 ## Automatically packaged extensions
 
-The actual packages are created by `buildGnomeExtensions.nix`, provided the correct arguments are fed into it. The important extension data is stored in `extensions.json`, one line/item per extension. That file is generated by running `update-extensions.py`. Furthermore, the automatic generated names are dumped in `collisions.json` for manual inspection. `extensionRenames.nix` contains provides new names for all extensions that collide.
+The actual packages are created by `buildGnomeExtension.nix`, provided the correct arguments are fed into it. The important extension data is stored in `extensions.json`, one line/item per extension. That file is generated by running `update-extensions.py`. Furthermore, the automatic generated names are dumped in `collisions.json` for manual inspection. `extensionRenames.nix` contains new names for all extensions that collide.
 
 ### Extensions updates
 
@@ -20,6 +20,7 @@ For GNOME updates,
 3. Update `supported_versions` in `./update-extensions.py` and re-run it
 4. Change `gnomeExtensions` to the new version
 5. Update `./extensionsRenames.nix` accordingly
+6. Update `all-packages.nix` accordingly (grep for `gnomeExtensions`)
 
 ## Manually packaged extensions