docs: Added plugins and development guide

docs/plugin_development.md

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+# Plugin Development Guide
+
+Plugins are first-party or third-party applications written to work directly with `bootstrap`. Unlike installers (or packages) which modify your system by compiling code, downloading binaries, and altering shell configuration files, **plugins are lazy-loaded scripts that execute within a sandboxed subshell**.
+
+This means downloading and invoking a plugin makes no system modifications other than caching the `.sh` file itself. They are fetched only the very first time you invoke them.
+
+## 1. Writing a Plugin Script
+
+A plugin is fundamentally a single Bash script. When executed by a user via `b <plugin_name>`, `bootstrap` runs the script in a subshell. This guarantees that any variables or state changes your plugin makes to the shell environment will not leak into the parent shell, preserving the integrity of the user's terminal.
+
+Because plugins execute within the `bootstrap` context, you automatically have access to all internal library functions (e.g., `lib/common.sh`, `lib/platform.sh`). For example, you can safely use logging functions like `log_info`, `log_success`, and `log_error`.
+
+Example `my_plugin.sh`:
+
+```bash
+#!/usr/bin/env bash
+# My Awesome Plugin
+
+# You can use bootstrap's built-in functions natively:
+log_info "Initializing awesome plugin..."
+
+if [ "${1:-}" == "--help" ]; then
+    echo "Usage: b my_plugin [args]"
+    exit 0
+fi
+
+log_success "Task completed successfully!"
+```
+
+## 2. Creating a Manifest
+
+For your plugin to be discoverable and dynamically updatable by `bootstrap`, you must provide a JSON manifest. `bootstrap` uses a robust, native Bash-based JSON parser to read this manifest.
+
+Create a JSON file (e.g., `plugins.json`) and host it publicly (e.g., as a GitHub raw URL).
+
+Example `plugins.json`:
+
+```json
+{
+  "plugins": {
+    "my_plugin": {
+      "version": "1.0.0",
+      "url": "https://raw.githubusercontent.com/yourusername/repo/main/my_plugin.sh",
+      "description": "An awesome plugin that prints logs"
+    }
+  }
+}
+```
+
+* **`version`**: The current semantic version of your plugin. When `bootstrap` detects a version change during `b up`, it automatically clears the cached `.sh` file, forcing a lazy re-download on the next invocation.
+* **`url`**: The raw, direct URL to your `.sh` plugin script. 
+
+## 3. Distribution
+
+To let users install your plugin, simply provide them the raw URL to your JSON manifest.
+
+Users will add it by running:
+
+```bash
+b plugin sources
+```
+
+They simply append your URL as a new line in the sources file. Once saved, `bootstrap` will automatically fetch your manifest and build a fast-lookup cache. The user can then immediately invoke your plugin:
+
+```bash
+b my_plugin
+```