docs: create readme

Author: SergioRibera

README.md

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+# GRHooks - Webhook Server Configuration
+
+GRHooks is a configurable webhook server that can execute commands or scripts in response to incoming webhook events. It supports multiple webhook configurations with flexible command execution options.
+
+## Install prebuilt binaries via shell script
+
+```sh
+bash <(curl -sSL https://raw.githubusercontent.com/RustLangES/grhooks/main/scripts/install.sh)
+```
+
+## Install prebuilt binaries via powershell script
+
+```sh
+powershell -ExecutionPolicy Bypass -c "$ProgressPreference='SilentlyContinue'; iex ((New-Object System.Net.WebClient).DownloadString('https://raw.githubusercontent.com/RustLangES/grhooks/main/scripts/install.ps1'))"
+```
+
+## Configuration File
+
+GRHooks uses a configuration file in TOML, YAML, or JSON format. The file should contain the server settings and webhook definitions.
+
+### Example Configuration (TOML)
+
+```toml
+port = 8080
+
+[[webhooks]]
+path = "deploy"
+secret = "mysecret123" # or "${{ env(\"MY_SECRET_FROM_ENV\") }}"
+events = ["push", "pull_request"]
+command = "echo 'Deployment triggered by ${{event.action}}'"
+
+[[webhooks]]
+path = "build"
+shell = ["/bin/bash", "-c"]
+script = "scripts/build.sh"
+events = ["create"]
+```
+
+## Configuration Options
+
+### Server Configuration
+
+| Field   | Type   | Description                   | Default | Required |
+| ------- | ------ | ----------------------------- | ------- | -------- |
+| port    | u16    | Port to listen on             | -       | Yes      |
+| verbose | String | Logging verbosity level (0-4) | "0"     | No       |
+
+### Webhook Configuration
+
+Each webhook is defined in the `webhooks` array with the following options:
+
+| Field   | Type                | Description                                                            | Required                             |
+| ------- | ------------------- | ---------------------------------------------------------------------- | ------------------------------------ |
+| path    | String              | URL path for the webhook                                               | No (defaults to /)                   |
+| secret  | Option<String>      | Secret for validating webhook signatures                               | No                                   |
+| events  | Vec<String>         | List of events this webhook should handle (use `["*"]` for all events) | Yes                                  |
+| shell   | Option<Vec<String>> | Custom shell and arguments to use for command execution                | No (defaults to `/bin/sh -c`)        |
+| command | Option<String>      | Command to execute when webhook is triggered                           | Either command or script must be set |
+| script  | Option<PathBuf>     | Path to script file to execute when webhook is triggered               | Either command or script must be set |
+
+## Template Variables
+
+Commands and scripts can use template variables that will be replaced with values from the webhook payload. Variables use the syntax `${{path.to.value}}`.
+
+> [!NOTE]
+> The template is redered using the [srtemplate](https://github.com/SergioRibera/srtemplate) template engine.
+
+### Common Variables
+
+- `${{event.type}}`: The event type that triggered the webhook
+
+## Running GRHooks
+
+### Command Line Usage
+
+```bash
+grhooks [-v...] /path/to/config.[toml|yaml|json]
+```
+
+Options:
+
+- `-v`: Increase verbosity (can be used multiple times)
+
+### Environment Variables
+
+- `GRHOOKS_MANIFEST_DIR`: Path to configuration file
+- `GRHOOKS_LOG`: Set logging verbosity (0-4 or trace, info, debug, warning, error)
+
+## Webhook Security
+
+When a `secret` is configured in the webhook:
+
+1. GRHooks will validate the `X-Hub-Signature-256` header
+2. Only requests with valid signatures will be processed
+3. The secret should match what's configured in your Git provider
+
+## Example Use Cases
+
+1. **Deployment Automation**:
+
+   ```toml
+   [[webhooks]]
+   path = "deploy-prod"
+   events = ["deployment"]
+   command = "kubectl set image deployment/myapp app=${{event.deployment.payload.image}}"
+   ```
+
+2. **CI/CD Pipeline**:
+
+   ```toml
+   [[webhooks]]
+   path = "build"
+   script = "scripts/ci-pipeline.sh"
+   events = ["push"]
+   ```
+
+3. **Notification System**:
+   ```toml
+   [[webhooks]]
+   path = "notify"
+   events = ["*"]
+   command = "curl -X POST -d '{\"text\":\"Event ${{event.type}} received\"}' $SLACK_WEBHOOK"
+   ```
+
+## Supported Webhook Providers
+
+GRHooks currently supports webhooks from:
+
+- GitHub
+
+Plans to support:
+
+- GitLab
+- Bitbucket