feat: Flat import of markdown repo

This is a flat (without history) import of (some of) the content
from our markdown module.

We've imported this without history because the repo contains our
blog posts and showcases posts content prior to porting them to strapi.

Since this contains many images, it would balloon the size of this repo
to import the full history.

Instead, please refer to the history of the (archived) markdown repo
at: https://github.com/freesewing/markdown

markdown/dev/guides/plugins/using-hooks/en.md

@@ -0,0 +1,59 @@
+---
+title: Using hooks
+order: 70
+---
+
+For each hook, your plugin should provide a method that takes the relevant data
+as its first argument. If data was passed when the hook was loaded, you will receive
+that as the second object.
+
+Remember that:
+
+ - The `insertText` hook will receive a locale and string and you should return a string.
+ - All other hooks receive an object. You don't need to return anything, but rather modify the object you receive.
+
+Let's look at an example:
+
+```js
+import myStyle from './style';
+import myDefs from './defs';
+import {name, version} from '../package.json';
+
+export default {
+  name,
+  version,
+  hooks: {
+    preRender: function(svg) {
+      if (svg.attributes.get("freesewing:plugin-"+name) === false) {
+        svg.style += myStyle;
+        svg.defs += myDefs;
+        svg.attributes.add("freesewing:plugin-"+name, version);
+      }
+    },
+    insertText: function(text) {
+      return text.toUpperCase();
+    }
+  }
+}
+```
+
+This is a complete plugin, ready to be published on NPM. It uses two hooks:
+
+ - `preRender` : We add some style and defs to our SVG
+ - `insertText` : We transfer all text to UPPERCASE
+
+<Note>
+
+###### Note that we avoid running our hook twice
+
+As you can see, the last thing we do in the `preRender` hook is set an attribute on
+the SVG tag with the name and version of our plugin.
+
+We check for this attribute when the `preRender` hook runs, thereby avoiding that
+our styles and defs will be added twice.
+
+It is good practice to wrap you hook methods in a call like this, because you have 
+no guarantee the user won't render your pattern more than once.
+
+</Note>
+