Add Pyxis user manual

[brothercorvo]

Summary

• add a user manual covering installation, controls, screens, settings, and troubleshooting
• document current runtime behavior and known limitations based on the firmware code
• link the new manual from the README

Testing

• not run (documentation only)

[greptile-apps]

Greptile Summary

This PR adds a user manual (docs/user-manual.md) and links it from README.md. All documented values were verified against the firmware source (main.cpp, SettingsScreen.cpp, ChatScreen.cpp) and are accurate. One P2 style suggestion was left regarding the version-specific (0.2) parenthetical in the controls section.

Confidence Score: 5/5

Safe to merge — documentation-only change with no code modifications.

No P0 or P1 findings. The single P2 comment is a style nit on a version qualifier. All factual claims in the manual were verified against the firmware source and are accurate.

No files require special attention.

Important Files Changed

Filename	Overview
README.md	Adds a Documentation section with a link to the new user manual; one-line change, no issues.
docs/user-manual.md	New 417-line user manual; content verified against firmware source for TCP defaults, LoRa options, timeout values, interval units, delivery indicators, and location-sharing options — all accurate. One version-specific parenthetical ("(0.2)") in the controls section is a minor style issue.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[User opens Pyxis] --> B[Conversations Screen]
    B --> C[Tap conversation]
    B --> D[Compose button]
    B --> E[Announces button]
    B --> F[Status button]
    B --> G[Map button]
    B --> H[Settings button]

    C --> I[Chat Screen]
    I --> J[Send message]
    I --> K[GPS / Location sharing]
    I --> L[LXST Voice Call]

    D --> M[New Message Screen]
    E --> N[Announce List Screen]
    F --> O[Status Screen]
    O --> P[QR Share Screen]
    G --> Q[Map Screen]
    H --> R[Settings Screen]
    R --> S[Propagation Nodes Screen]

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Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
docs/user-manual.md:78
The parenthetical `(0.2)` ties these behaviors to a specific firmware version, which will read as confusing or stale for anyone on a different version. The behaviors themselves (long-press to delete/copy/paste) are general UI interactions that apply to the current build, so the version qualifier can simply be removed.

```suggestion
Useful behaviors:
```

_{Reviews (2): Last reviewed commit: "Update user manual map instructions" | Re-trigger Greptile}