docs: add request-lifecycle to the documentation + new homepage

[francescovallone]

Description

Add a request-lifecycle page with the needed information to understand what Serinus is doing, for the hooks see #18. Also add new homepage for the Serinus Documentation.

Fixes #15

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

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