Add remark-ins to list of plugins

Closes GH-1129.

Reviewed-by: Christian Murphy <christian.murphy.42@gmail.com>
Reviewed-by: Remco Haszing <remcohaszing@gmail.com>
Reviewed-by: Titus Wormer <tituswormer@gmail.com>

doc/plugins.md

@@ -163,6 +163,8 @@ The list of plugins:
     — prefix relative image paths with an absolute URL
 *   🟢 [`remark-inline-links`](https://github.com/remarkjs/remark-inline-links)
     — change references and definitions to links and images
+*   🟢 [`remark-ins`](https://github.com/ipikuka/remark-ins)
+    — add ins element for inserted texts opposite to deleted texts
 *   🟢 [`remark-join-cjk-lines`](https://github.com/purefun/remark-join-cjk-lines)
     — remove extra space between CJK Characters.
 *   ⚠️ [`remark-kbd`](https://github.com/zestedesavoir/zmarkdown/tree/HEAD/packages/remark-kbd#readme)