docs: add debugging page

This explains how I've designed Slyde, and what to do in case of an error.

Author: Tygo-van-den-Hurk

docs/debugging.md

@@ -0,0 +1,15 @@
+# Debugging
+
+Slyde is build on the mentality of "let it crash". I will try to make Slyde crash when it reaches an invalid state, and mention where this mistake in the document was. I try to provide you with a path to the invalid node. 
+
+For example this obviously does not make sense:
+
+```XML
+<presentation title="outer presentation">
+  <presentation title="inner presentation" />
+</presentation>
+```
+
+So, you'll receive an error along the lines of `"Expected slides at ${path} but found presentation"` where path is the path to the inner presentation. These paths are based on [xpath](https://www.w3schools.com/xml/xpath_intro.asp), a XML query language. This makes sure we are all on the same page, and might make creating IDE extensions easier later.
+
+In case you do not get a path, that is a shame. Feel free to [open an issue](https://github.com/Tygo-van-den-Hurk/Slyde/issues/new) and I will look into it.