Update machine option on the README (#71)

* set machine as option

* rename machine as system

* fix env var names

* fix env var names

* fix shortoption

* update readme

README.md

@@ -71,22 +71,25 @@ firecrest submit-template --help
 
 Some basic examples:
 ```bash
+# Get the parameters of different microservices of FirecREST
+firecrest parameters
+
 # Get the available systems
 firecrest systems
 
-# Get the parameters of different microservices of FirecREST
-firecrest parameters
+# Set the environment variable to specify the name of the system
+export FIRECREST_SYSTEM="cluster"
 
 # List files of directory
-firecrest ls cluster1 /home
+firecrest ls /home
 
 # Submit a job
-firecrest submit cluster script.sh
+firecrest submit script.sh
 
 # Upload a "small" file (you can check the maximum size in `UTILITIES_MAX_FILE_SIZE` from the `parameters` command)
-firecrest upload --type=direct cluster local_file.txt /path/to/cluster/fs
+firecrest upload --type=direct local_file.txt /path/to/cluster/fs
 
 # Upload a "large" file
-firecrest upload --type=external cluster local_file.txt /path/to/cluster/fs
+firecrest upload --type=external local_file.txt /path/to/cluster/fs
 # You will have to finish the upload with a second command that will be given in the output
 ```