readme: add deployment documentation

Author: Bnyro

README.md

@@ -1,3 +1,16 @@
 # [LibreTube Website](https://libre-tube.github.io)
 
 Feel free to report bugs concerning the website or suggest changes or features in the issues tab.
+
+## Local deployment
+First, install the required dependencies
+```sh
+npm run install
+```
+
+Then, you can run the app with
+```sh
+npm run dev
+```
+
+For more information, please see the [Astro documentation](https://docs.astro.build/en/develop-and-build/).