Add textobject docs

book/src/keymap.md

@@ -147,14 +147,17 @@ Jumps to various locations.
 ## Match mode
 
 Enter this mode using `m` from normal mode. See the relavant section
-in [Usage](./usage.md#surround) for an explanation about surround usage.
+in [Usage](./usage.md) for an explanation about [surround](./usage.md#surround)
+and [textobject](./usage.md#textobject) usage.
 
 | Key              | Description                                     |
 | -----            | -----------                                     |
 | `m`              | Goto matching bracket                           |
 | `s` `<char>`     | Surround current selection with `<char>`        |
 | `r` `<from><to>` | Replace surround character `<from>` with `<to>` |
 | `d` `<char>`     | Delete surround character `<char>`              |
+| `a` `<object>`   | Select around textobject                        |
+| `i` `<object>`   | Select inside textobject                        |
 
 ## Object mode
 

book/src/usage.md

@@ -24,3 +24,19 @@ It can also act on multiple seletions (yay!). For example, to change every occur
 - `mr([` to replace the parens with square brackets
 
 Multiple characters are currently not supported, but planned.
+
+## Textobjects
+
+Currently supported: `word`, `surround`.
+
+![textobject-demo](https://user-images.githubusercontent.com/23398472/124231131-81a4bb00-db2d-11eb-9d10-8e577ca7b177.gif)
+
+- `ma` - Select around the object (`va` in vim, `<alt-a>` in kakoune)
+- `mi` - Select inside the object (`vi` in vim, `<alt-i>` in kakoune)
+
+| Key after `mi` or `ma` | Textobject selected      |
+| ---                    | ---                      |
+| `w`                    | Word                     |
+| `(`, `[`, `'`, etc     | Specified surround pairs |
+
+Textobjects based on treesitter, like `function`, `class`, etc are planned.