docs: change README

[amandahla]

Applicable spec:

Overview

This PR changes README default file.

• Add introduction
• Add architecture diagram
• Fix links

Rationale

Add README to the charm repo.

Juju Events Changes

Module Changes

Library Changes

Checklist

• The charm style guide was applied
• The contributing guide was applied
• The changes are compliant with ISD054 - Managing Charm Complexity
• The documentation is generated using src-docs
• The documentation for charmhub is updated
• The PR is tagged with appropriate label (urgent, trivial, complex)

No charmhub available yet.

[github-actions]

Test coverage for 0cdc949

Name           Stmts   Miss Branch BrPart  Cover   Missing
----------------------------------------------------------
src/charm.py      26      5      0      0    81%   48-52
----------------------------------------------------------
TOTAL             26      5      0      0    81%

Static code analysis report

Run started:2024-09-09 14:22:51.285601

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 117
  Total lines skipped (#nosec): 0
  Total potential issues skipped due to specifically being disabled (e.g., #nosec BXXX): 0

Run metrics:
  Total issues (by severity):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
  Total issues (by confidence):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
Files skipped (0):