Update docs

[erinecon]

Overview

Small changes to the documentation that are specific to the jenkins-agent-k8s-operator charm.

Rationale

• Index: Moved sections around to make it more consistent with other charms
• How-to guide: Fixed capitalisation

Juju Events Changes

None

Module Changes

None

Library Changes

None

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)

[github-actions]

Test coverage for 9fb9ab2

Name              Stmts   Miss Branch BrPart  Cover   Missing
-------------------------------------------------------------
src/agent.py         60      0     12      0   100%
src/charm.py         57      0     10      0   100%
src/metadata.py       8      0      0      0   100%
src/pebble.py        23      0      0      0   100%
src/server.py        50      0     12      0   100%
src/state.py         66      0     12      0   100%
-------------------------------------------------------------
TOTAL               264      0     46      0   100%

Static code analysis report

Run started:2024-09-06 18:39:53.019129

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 1667
  Total lines skipped (#nosec): 1
  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):