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/howtos/design/slash-spread/en.md

@@ -0,0 +1,46 @@
+---
+title: Slash and spread
+for: developers
+about: Slash and spread is easy enough on paper, here's how to do it in code
+---
+
+<Note>
+
+##### See this example in our source code
+
+ - [packages/jaeger/src/front.js](https://github.com/freesewing/freesewing/blob/8474477911daed3c383700ab29c9565883f16d66/packages/jaeger/src/front.js#L64)
+
+</Note>
+
+When we _slash and spread_ a pattern, we cut out a triangle, and then rotate it
+around the tip of the triangle.
+
+And that's exactly what we do in code. We just need to know:
+
+ - What point we want to rotate around
+ - Which points we want to rotate
+ - By how much we want to rotate
+
+```js
+let rotate = [
+  'splitEdge',
+  'neckEdge',
+  'cfNeck',
+  'cfNeckCp1',
+  'neckCp2Front',
+  'neck',
+  'shoulder',
+  'shoulderCp1',
+  'armholePitchCp2',
+  'armholePitch',
+  'armholePitchCp1',
+  'armholeHollowCp2',
+  'armholeHollow',
+  'armholeHollowCp1',
+  'splitCp2',
+  'frontNeckCpEdge'
+]
+for (let p of rotate) {
+  points[p] = points[p].rotate(options.chestShapingMax * options.chestShaping * -1, points.split)
+}
+```