docs: Add initial README for the Foundry VTT session tracker module.

README.md

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+# Session Tracker for Foundry VTT
+
+A lightweight, draggable session tracker for Foundry VTT V13.
+
+## Features
+
+- **Manual Tracking**: Easily increment or decrement the session number with +/- buttons.
+- **Auto-Increment**: Automatically increment the session count when a specific user (e.g., the GM or a key player) logs in for the first time in a day.
+- **Draggable Interface**: Place the tracker anywhere on your canvas; its position is saved per client.
+- **Customizable Scale**: Adjust the size of the tracker to fit your screen and preference.
+- **Player Visibility**: Players can choose whether they can see the tracker.
+
+## Installation
+
+To install the module, use the following manifest URL in the Foundry VTT Setup screen:
+
+```
+https://github.com/cptn-cosmo/fvtt-session-tracker/releases/latest/download/module.json
+```
+
+## Usage
+
+### GM Controls
+- **Increment/Decrement**: Click the **+** or **-** buttons on the tracker to change the session number.
+- **Drag and Drop**: Click and drag the tracker to reposition it.
+
+### Settings
+The tracker can be configured in the **Module Settings** tab:
+- **Current Session Number**: Manually set the session count.
+- **Automate Session Tracking**: Toggle auto-increment on login.
+- **Trigger User**: Select which user's login triggers the auto-increment.
+- **Show Session Tracker**: Toggle visibility of the tracker for yourself.
+- **Tracker Scale**: Scale the tracker from 0.5x to 2.0x.
+
+## Compatibility
+- Verified for Foundry VTT **Version 13**.