docs: update shared setup

Author: lowlighter

.github/readme/imgs/setup_shared.dark.png

@@ -1,19 +1,37 @@
-# 💕 Using the shared instance (~1 min setup, but with limitations)
+# 💕 Using the shared instance (~1 min)
 
-For convenience, you can use the shared instance available at [metrics.lecoq.io](https://metrics.lecoq.io) without any additional setup.
+For convenience, a free shared instance is available at [metrics.lecoq.io](https://metrics.lecoq.io) without any additional setup.
 
-```markdown
-![Metrics](https://metrics.lecoq.io/my-github-user)
-```
+## 0️ Setup a personal repository
+
+Create a repository with the same name as your GitHub login (if it doesn't exist).
+
+![Setup personal repository](/.github/readme/imgs/setup_personal_repository.png)
+
+Its `README.md` will be displayed on your user profile:
+
+![GitHub Profile Example](/.github/readme/imgs/example_github_profile.png)
+
+## 2️ Configure *metrics*
+
+Visit [metrics.lecoq.io](https://metrics.lecoq.io) and start playing around!
 
-This is mostly intended for previews, to enjoy all features consider using GitHub Action instead.
-Availability is not guaranteed.
+> ⚠️ Some plugins are not available on the web instance. Consider using [GitHub action](https://github.com/marketplace/actions/metrics-embed) to enjoy all features!
 
-To ensure service availability, shared instance has a few limitations:
-  * Images are cached for 1 hour
-    * Rendered metrics **won't be updated** during this time window when queried
-    * You can manually update rendering again your metrics on [metrics.lecoq.io](https://metrics.lecoq.io)
-  * A rate limiter is enabled to prevent denial of service (it doesn't affect already cached metrics)
-  * Some plugins may not be available
+![metrics.lecoq.io](/.github/readme/imgs/setup_shared.light.png#gh-light-mode-only)
+![metrics.lecoq.io](/.github/readme/imgs/setup_shared.dark.png#gh-dark-mode-only)
+
+> ⚠️ This service is hosted on a small server that I rent. It is provided free of charge so please be gentle with it 😅 Availability not guaranteed!
+
+> 💕 If you really enjoy this service, consider [sponsoring me](https://github.com/sponsors/lowlighter) to help me cover server costs!
+
+## 3️ Add images to your profile `README.md`
+
+Update profile `README.md` to include rendered image.
+
+*Example: add rendered image with markdown*
+```markdown
+![Metrics](https://metrics.lecoq.io/username)
+```
 
-Service is provided free of charge, so please be gentle with it 🙂
+> ⚠️ Images are cached for 1 hour after being rendered. They **won't be updated** during this time window when queried again. However it is possible to manually update them by using [metrics.lecoq.io](https://metrics.lecoq.io) again