Update project README.md

- Include a brief description of the client architecture (SSR/Proxy to Fractal)
- Include notes on .env.development default development configuration file

README.md

@@ -32,12 +32,20 @@ npm install
 
 ## Web client startup
 
-Create a `.env` file where you set the relevant environment variables. At the moment this includes a single variable:
+The project comes with a default `.env.development` development environment file.
+In this file are present a set of default values for the environment variables that are used by the application.
+The default values are set to work with a local instance of a fractal-server.
+
+Specifically, a fractal server is expected to run on `http://localhost:8000` as stated by the `FRACTAL_SERVER_HOST` variable.
+
+If you want to run the application with a different fractal server instance, you can create a `.env.development.local` file
+and override, for instance, the `FRACTAL_SERVER_HOST` variable with the address of your server instance, e.g.
+
 ```
-PUBLIC_FRACTAL_SERVER_HOST=http://127.0.0.1:8000
+FRACTAL_SERVER_HOST=http://localhost:8888
 ```
 
-Run the application via
+Run the client application via
 ```bash
 npm run dev -- --open
 ```
@@ -57,6 +65,12 @@ For user experience reasons, it is suggested to set the `JWT_EXPIRE_SECONDS=8460
 
 **Note**: The [example_server_startup folder](tests/data/example_server_startup) contains an example of how to install and startup a `fractal-server` instance.
 
+# Client architecture
+
+The client is a Svelte application that uses [SvelteKit](https://kit.svelte.dev) as a framework.
+The application is composed of a set of pages that are rendered by a node server and served to a client browser.
+The node server acts as a proxy to the fractal server, forwarding the requests to the server and returning the responses to the client.
+
 # Contributors
 
 Fractal was conceived in the Liberali Lab at the Friedrich Miescher Institute for Biomedical Research and in the Pelkmans Lab at the University of Zurich (both in Switzerland). The project lead is with [@gusqgm](https://github.com/gusqgm) & [@jluethi](https://github.com/jluethi). The core development is done under contract by [eXact lab S.r.l.](exact-lab.it).