docs: update README for Nextflow plugin registry compliance (#55)

## Summary

- Rename "Quick Start" → "Get Started" to match the registry's required
section names
- Use absolute GitHub URL for the notification screenshot so it renders
on the registry
- Add "Examples" section with bot configuration snippets (bot-only, no
webhooks)

The Nextflow plugin registry requires README.md to include **Summary**,
**Get Started**, **Examples**, and **License** sections. The
`releasePlugin` Gradle task already sends the README as the
documentation field — these changes ensure it passes registry validation
and renders correctly.

Author: adamrtalbot

README.md

@@ -14,7 +14,7 @@ Get Slack notifications for your Nextflow workflows — automatically notified w
 - **Threading, Reactions, and Progress Updates** — Keep channels organized
 - **Seqera Platform Integration** — One-click navigation to your runs
 
-## Quick Start
+## Get Started
 
 Add to your `nextflow.config`:
 
@@ -34,7 +34,7 @@ slack {
 
 Run your pipeline — you'll get Slack notifications automatically:
 
-![Default notifications](./docs/images/nf-slack-00.png)
+![Default notifications](https://raw.githubusercontent.com/seqeralabs/nf-slack/main/docs/images/nf-slack-00.png)
 
 See the [Setup Guide](https://seqeralabs.github.io/nf-slack/latest/getting-started/setup/) for bot and webhook configuration options.
 
@@ -46,6 +46,40 @@ See the [Setup Guide](https://seqeralabs.github.io/nf-slack/latest/getting-start
 - **[API Reference](https://seqeralabs.github.io/nf-slack/latest/reference/api/)** — All configuration options
 - **[Contributing](docs/CONTRIBUTING.md)** — Development setup and guidelines
 
+## Examples
+
+Here are a few common configurations to get you started:
+
+**Basic bot notifications:**
+
+```groovy
+slack {
+    enabled = true
+    bot {
+        token = 'xoxb-your-bot-token'
+        channel = 'pipeline-results'
+    }
+}
+```
+
+**Threaded messages with start, complete, and error events:**
+
+```groovy
+slack {
+    enabled = true
+    bot {
+        token = 'xoxb-your-bot-token'
+        channel = 'pipeline-results'
+    }
+    useThreads = true
+    onStart.send = true
+    onComplete.send = true
+    onError.send = true
+}
+```
+
+See the [Examples Gallery](https://seqeralabs.github.io/nf-slack/latest/examples/gallery/) for more copy-paste configurations.
+
 ## Support
 
 - [Report bugs](https://github.com/seqeralabs/nf-slack/issues)