goliothctl: add tutorial section on apikey login

Updates the authentication CLI tutorial section to show API key login
as an option.

Author: soelgary

docs/_partials-common/login-flow.md

@@ -1,5 +1,11 @@
 ### Start login flow
 
+You can authenticate the CLI in two ways:
+1. User credentials
+2. Project API key
+
+### Option 1: User credentials (default)
+
 Run the command:
 
 ```
@@ -8,6 +14,16 @@ goliothctl login
 
 This will redirect you to your default browser where you can login or create an account on our system.
 
-### Create account or login with an existing one
+#### Create account or login with an existing one
 
 After successfully authenticating into our system, you should be redirected to a success page and the CLI will be authenticated properly.
+
+### Option 2: Project API key
+
+Run the command:
+
+```
+goliothctl login --apiKey <api_key>
+```
+
+This method skips the browser flow and authenticates the CLI directly.