Update README.md

README.md

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 # FundSimulatorRS
 FundSimulatorRS is a versatile Rust-based program for simulating the behaviour of index funds through easy-to-configure settings.
 
+
 ## Usage
-The actual implementation run on the CLI, being customizable by the following parameters:
-- `--amount` or `-a`: Initial amount for the investing
-- `--interest` or `-i`: Annual percentage of interest
-- `--years` or `-y`: Investment years
-- `--contributions` or `-c`: Extra contribution per year
+The application can run in two modes: server and CLI. Both modes use a JSON file as input. It must include the following information:
+- `deposit`: Integer representing the initial deposit. 
+- `years`: Integer representing the number of years for the simulation.
+- `return_rates`: Float or list of floats. If a single float, then the same return rate is applied for all the years. Otherwise, the number of elements in the list must be equal to the number of years.
+- `annual_contributions`: Float or list of floats. If a single float, then the same annual contribution is applied for all the years. Otherwise, the number of elements in the list must be equal to the number of years.
+
+### CLI mode
+```
+cargo run -- --mode cli --config-file example.json
+```
+
+### Server mode
+Run the following command or `docker compose run` to start the server.
+```
+cargo run -- --mode server
+```
+It will be listening on port 3000 by default.
+The endpoint is `/simulate` and you need to pass the config json in the payload.