Add demo environment information to docs and README

Introduced details about the public demo environment, including URL, credentials, and reset schedule, to the README, and documentation index. This helps users try Endurain before installation and clarifies demo limitations.

README.md

@@ -15,6 +15,18 @@
   <img src="screenshot_01.png" alt="Endurain Screenshot">
 </div>
 
+## 🚀 Try the Demo
+
+Experience Endurain without installation:
+
+**Demo URL:** [https://demo.endurain.com](https://demo.endurain.com)
+
+- **Username:** `admin`
+- **Password:** `admin`
+- **Reset Schedule:** Daily at midnight (Europe/Lisbon timezone)
+
+> ⚠️ **Note:** The demo environment resets every day. Do not store important data.
+
 ## Table of Contents
 
 - [Endurain documentation](https://docs.endurain.com)

docs/index.md

@@ -27,6 +27,19 @@
   </p>
 </div>
 
+## 🚀 Try the Demo
+
+Experience Endurain without installation:
+
+**Demo URL:** [https://demo.endurain.com](https://demo.endurain.com)
+
+- **Username:** `admin`
+- **Password:** `admin`
+- **Reset Schedule:** Daily at midnight (Europe/Lisbon timezone)
+
+!!! warning "Demo Environment"
+    The demo environment resets every day at midnight. Do not store important data or expect persistence.
+
 ## What is Endurain?
 
 Endurain is a self-hosted fitness tracking service designed to give users full control over their data and hosting environment. Built with: