Installation guide added

Installation.md

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+This guide explains how to install Sentri on a Linux server.
+# Requirements
+Before continuing, make sure your server meets the following requirements:
+- A Linux server (Linux is officially tested and supported)
+- Basic Linux and web hosting experience
+- A web server of your choice (Apache, Nginx, Caddy, etc.)
+- MariaDB or MySQL
+- PHP 8.3 or newer
+- Git installed on the server
+
+>[!info]
+>This guide uses `/var/www/sentri/` as the installation directory. You can change this to any location you prefer.
+# Installation
+
+## Configure the document root
+Sentri stores all publicly accessible files inside the `pub/` directory.
+If your current virtual host document root is:
+```
+/var/www/sentri/
+```
+Change it to:
+```
+/var/www/sentri/pub/
+```
+After updating the document root, reload or restart your web server.
+## Download the Sentri files
+Run the following commands to download the latest version of Sentri:
+```bash
+cd /var/www/sentri/
+
+git clone https://gitea.mooij.me/meteo/Sentri.git Sentri
+
+mv Sentri/* .
+mv Sentri/.[!.]* . 2>/dev/null
+
+rmdir Sentri
+```
+## Database setup
+Log in to MariaDB/MySQL and create the database and user:
+```sql
+CREATE DATABASE sentri;  
+CREATE USER 'sentri'@'localhost' IDENTIFIED BY 'your_secure_password_here';  
+GRANT ALL PRIVILEGES ON sentri.* TO 'sentri'@'localhost';  
+FLUSH PRIVILEGES;
+```
+
+Next, import the database schema:
+```bash
+mariadb -u sentri -p sentri < /var/www/sentri/install.sql
+```
+When prompted, enter the password for the `sentri` database user.
+## Configuring
+Copy the example configuration file:
+```bash
+cp /var/www/sentri/pub/config-sample.php /var/www/sentri/pub/config.php
+```
+Then edit the configuration file and update the database credentials:
+```
+/var/www/sentri/pub/config.php
+```
+# First Login
+Open your website in a browser and log in with the default credentials:
+```
+Username: superuser
+Password: changethispassword
+```
+
+> [!WARNING]
+> After logging in change the superuser password!
+# Getting started 
+After completing the installation, continue with the [[Getting Started]] guide to configure and begin using Sentri.