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/prerequisites/coordinate-system/en.md

@@ -0,0 +1,24 @@
+---
+title: Coordinate system
+order: 30
+---
+
+In FreeSewing -- and in SVG -- coordinates are like text in a book. 
+You start at the top on the left side, and going to the right 
+and downwards means going ahead.
+
+<Example part="docs_coords" caption="The SVG coordinate system" /> 
+
+Which means that on the X-axis, `20` is further to the right than `10`.  
+Likewise, on the Y-axis, `50` is lower than `20`.
+
+<Note>
+
+The Y-axis is inverted in many drawing programs, with the origin
+`(0,0)` being the lower left corner, rather than the upper left corner.
+
+This is a common point of confusion so keep in mind that the Y-axis may
+not behave as you would have intuitively expected.
+
+</Note>
+