Add a link to Markdown's documentation.

README.md

@@ -2,6 +2,11 @@
 
 A flat-file database of courses in multiple languages.
 
+## Documentation
+
+- Read the extensive [Markdown documentation](https://docs.gitlab.com/ee/user/markdown.html).
+
+-----
 
 ### Mermaid demo
 
@@ -31,3 +36,11 @@ graph LR
 
   Student --> |reads| File
 ```
+
+### Table demo
+
+| A | B |   | D |   |
+|---|---|---|---|---|
+|   |   |   |   |   |
+|   |   | X |   |   |
+|   |   | X |   | _test_  |