Add tutorial and requirements to index.md

A new tutorial was added to the main documentation page, it covers the goal and the requirements for setting up the Music API. DRF and Django are introduced as the main tools in this tutorial, replacing the sequence diagram.

Author: lipemorais

docs/sample.md

@@ -2,6 +2,13 @@
 
 For full documentation visit [mkdocs.org](https://www.mkdocs.org).
 
+## mermaid
+
+```mermaid
+sequenceDiagram
+    Alice ->> Bob: Hello Bob, how are you?
+```
+
 ## Code Annotation Examples
 
 ### Codeblocks