minor fixes

docs/src/docPages/api/extensions/horizontal-rule.md

@@ -3,6 +3,15 @@ Use this extension to render a `<hr>` HTML tag. If you pass `<hr>` in the editor
 
 Type three dashes (`---`) or three underscores and a space (`___ ​`) at the beginning of a new line and it will magically transform to a horizontal rule.
 
+## Installation
+```bash
+# With npm
+npm install @tiptap/extension-horizontal-rule
+
+# Or: With Yarn
+yarn add @tiptap/extension-horizontal-rule
+```
+
 ## Options
 | Option | Type   | Default | Description                                  |
 | ------ | ------ | ------- | -------------------------------------------- |

docs/src/docPages/guide/custom-extensions.md

@@ -1,9 +1,7 @@
 # Custom Extensions
-
 Let’s extend tiptap with a custom extension!
 
 ## Option 1: Change defaults
-
 Let’s say you want to change the keyboard shortcuts for the bullet list. You should start by looking at [the source code of the `Bold` extension](https://github.com/ueberdosis/tiptap-next/blob/main/packages/extension-bold/index.ts) and find the default you’d like to change. In that case, the keyboard shortcut.
 
 ```js
@@ -28,4 +26,4 @@ new Editor({
 
 ## Option 2: Extend existing extensions
 
-## Option 3: Start from scratch
+## Option 3: Start from scratch