chore: proposal to update the terminal output for the login (#140)

Making it easier for users to understand the login functionality.

copernicusmarine/core_functions/credentials_utils.py

@@ -91,7 +91,15 @@ def _load_credential_from_motu_configuration_file(
 def _retrieve_credential_from_prompt(
     credential_type: Literal["username", "password"], hide_input: bool
 ) -> str:
-    return click.prompt(credential_type, hide_input=hide_input)
+    if credential_type == "username":
+        logger.info(
+            "Downloading CMEMS data requires a Copernicus Marine username "
+            "and password, sign up for free at:"
+            " https://data.marine.copernicus.eu/register"
+        )
+    return click.prompt(
+        "copernicusmarine " + credential_type, hide_input=hide_input
+    )
 
 
 def _retrieve_credential_from_environment_variable(

tests/test_command_line_interface.py

@@ -861,7 +861,12 @@ def test_login_is_prompt_when_configuration_file_doest_not_exist(
             command, env=environment_without_crendentials
         )
         assert self.output.returncode == 1
-        assert b"username:" in self.output.stdout
+        assert (
+            b"Downloading CMEMS data requires a Copernicus Marine username "
+            b"and password, sign up for free at:"
+            b" https://data.marine.copernicus.eu/register"
+        ) in self.output.stderr
+        assert b"copernicusmarine username:" in self.output.stdout
 
     def test_login_command(self, tmp_path):
         self.check_credentials_username_specified_password_prompt(tmp_path)