docs: add manpage in markdown and roff format

[CoolatMax]

Description

This PR addresses #68 by adding comprehensive manpages for the GreenhousePython CLI.

To ensure the documentation is both maintainable and system-ready, I have provided:

1. docs/man/greenhouse.md: A human-readable Markdown source for easy future edits.
2. docs/man/greenhouse.1: A compiled Roff-formatted manpage for Linux man system integration.

Technical Audit & Discoveries

While drafting this manual, I performed a source code audit of main.py to identify undocumented requirements:

• Configuration Requirement: Added documentation for the mandatory cfg.txt file and its required keys (beds, file_name_prefix).
• Interface Structure: Documented the four primary control modules: Camera, Water (per-bed), Light, and Misc.
• Dependency Context: Included information regarding the GTK4 and Typer foundations of the app.

How to Test

You can verify the formatting of the generated manpage by running the following in a terminal:

man ./docs/man/greenhouse.1

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How does Manpages looks in the terminal:

Screenshot 1

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