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/reference/api/snippet/attr/en.md

@@ -0,0 +1,31 @@
+---
+title: attr()
+---
+
+```js
+Snippet snippet.attr(
+  string name, 
+  mixed value, 
+  bool overwrite = false
+)
+```
+
+This `Snippet.attr()` method calls [`Attributes.add()`](./attributes#add) under the hood, 
+but returns the Snippet object.  This allows you to chain different calls together.
+
+If the third parameter is set to `true` it will call [`Attributes.set()`](./attributes#set) instead, 
+thereby overwriting the value of the attribute.
+
+<Example
+  part="snippet_attr"
+  caption="An example of the Snippet.attr() method"
+/>
+
+```js
+let { Point, points, Snippet, snippets } = part.shorthand();
+
+points.anchor = new Point(50, 15);
+snippets.demo = new Snippet("logo", points.anchor)
+  .attr("data-scale", 0.8)
+  .attr("data-rotate", 180);
+```