docs: add documentation for prev-next links (#889)

Co-authored-by: Percy Ma <kecrily@gmail.com>
Co-authored-by: Divyansh Singh <40380293+brc-dd@users.noreply.github.com>

docs/guide/theme-prev-next-link.md

@@ -1,3 +1,53 @@
 # Prev Next Link
 
-Documentation coming soon...
+Prev or Next Link allows you to add buttons at the end of each page that allow you to go to the previous or next topic. To enable it, add `themeConfig.prev` or `themeConfig.next` to your configuration.
+
+
+## prev
+
+- Type: `NavLink | string`
+
+- Details:
+
+  Specify the link of the previous page.
+
+  If you don't set this frontmatter, the link will be inferred from the sidebar config.
+
+  To configure the prev link manually, you can set this frontmatter to a `NavLink` object or a string:
+
+  - A `NavLink` object should have a `text` field and a `link` field.
+  - A string should be the path to the target page file. It will be converted to a `NavLink` object, whose `text` is the page title, and `link` is the page route path.
+
+- Example:
+
+```md
+---
+# NavLink
+prev:
+  text: Get Started
+  link: /guide/getting-started.html
+
+# NavLink - external url
+prev:
+  text: GitHub
+  link: https://github.com
+
+# string - page file path
+prev: /guide/getting-started.md
+
+# string - page file relative path
+prev: ../../guide/getting-started.md
+---
+```
+
+## next
+
+- Type: `NavLink | string`
+
+- Details:
+
+  Specify the link of the next page.
+
+  If you don't set this frontmatter, the link will be inferred from the sidebar config.
+
+  The type is the same as [prev](#prev) frontmatter.