Add remark-jargon to list of plugins

Closes GH-441.

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

doc/plugins.md

@@ -110,6 +110,8 @@ See [Creating plugins][create] below.
     — add an improved image syntax
 *   [`remark-inline-links`](https://github.com/remarkjs/remark-inline-links)
     — change references and definitions to links and images
+*   [`remark-jargon`](https://github.com/freesewing/freesewing/tree/develop/packages/remark-jargon)
+    — inserts definitions for jargon terms
 *   [`remark-kbd`](https://github.com/zestedesavoir/zmarkdown/tree/master/packages/remark-kbd#readme)
     — custom syntax for keyboard keys (new node type, rehype compatible)
 *   [`remark-kbd-plus`](https://github.com/twardoch/remark-kbd-plus)