Minor docs tweaks (#71)

- Better broken link error checking
- Link to Mermaid

docs/README.md

@@ -1,6 +1,7 @@
 # Corso documentation
 
 Corso documentation uses [Docusaurus 2](https://docusaurus.io/), a modern static website generator.
+[Mermaid](https://mermaid-js.github.io/mermaid/) provides support for native diagrams in Markdown.
 
 ## Requirements
 

docs/docusaurus.config.js

@@ -11,7 +11,7 @@ const config = {
   url: 'https://corsobackup.io',
   baseUrl: '/',
   onBrokenLinks: 'throw',
-  onBrokenMarkdownLinks: 'warn',
+  onBrokenMarkdownLinks: 'throw',
   favicon: 'img/corso.svg',
 
   // GitHub pages deployment config.