cfg and README update

README.md

@@ -6,3 +6,13 @@ After cloning, run
 git submodule init
 git submodule update
 ```
+
+# Using the `.cargo/config.toml` file
+
+Use the following command to have a starting `config.toml` file
+
+```sh
+cp .cargo/def-config.toml .cargo/config.toml
+```
+
+You then can adapt the `config.toml` to your needs