Additions to 'themes' section of docs (#2098)

* Added more descriptions to the themes part of the docs

* Add more descriptions to themes section of the docs

* capitalised first letters of descriptions in docs

Co-authored-by: Joe Mckay <jm@pop-os.localdomain>

book/src/themes.md

@@ -213,19 +213,19 @@ These scopes are used for theming the editor interface.
 | `ui.cursor.select`       |                                                |
 | `ui.cursor.match`        | Matching bracket etc.                          |
 | `ui.cursor.primary`      | Cursor with primary selection                  |
-| `ui.linenr`              |                                     |
-| `ui.linenr.selected`     |                                     |
+| `ui.linenr`              | Line numbers                                   |
+| `ui.linenr.selected`     | Line number for the line the cursor is on      |
 | `ui.statusline`          | Statusline                                     |
 | `ui.statusline.inactive` | Statusline (unfocused document)                |
-| `ui.popup`               |                                     |
-| `ui.popup.info`          |                                     |
-| `ui.window`              |                                     |
-| `ui.help`                |                                     |
-| `ui.text`                |                                     |
+| `ui.popup`               | Documentation popups (e.g space-k)             |
+| `ui.popup.info`          | Prompt for multiple key options                |
+| `ui.window`              | Border lines separating splits                 |
+| `ui.help`                | Description box for commands                   |
+| `ui.text`                | Command prompts, popup text, etc.              |
 | `ui.text.focus`          |                                                |
-| `ui.text.info`           |                                     |
-| `ui.menu`                |                                     |
-| `ui.menu.selected`       |                                     |
+| `ui.text.info`           | The key: command text in `ui.popup.info` boxes |
+| `ui.menu`                | Code and command completion menus              |
+| `ui.menu.selected`       | Selected autocomplete item                     |
 | `ui.selection`           | For selections in the editing area             |
 | `ui.selection.primary`   |                                                |
 | `warning`                | Diagnostics warning (gutter)                   |