fixed a typo in README

README.md

@@ -59,15 +59,16 @@ xhost +SI:localuser:$(id -un)
 You can use the following shortcut function and place it to your `~/.bash_aliases` file:
 
 ```sh
-function docker_helper() {{
+function docker_helper() {
     pushd ~/docker/$1
     docker-compose rm -fa "$1"
     docker-compose run -d --name "$1" "$@"
     popd
-}}
+}
+
 function steam() {
     docker_helper $FUNCNAME $@
-}}
+}
 ```
 
 Then just use `steam` command to run Steam in docker.