📝 docs(login.mdx): add documentation for login functionality in Langflow

The login functionality in Langflow serves to authenticate users and protect sensitive routes in the application. This commit adds documentation for the login functionality, including information about the enhanced login mechanism introduced in version 0.5. It explains the environment variables that are crucial in configuring the login settings and provides instructions on how to set them securely. It also covers the command-line interface for managing superusers and provides details on the sign-up process and profile settings for users. Screenshots are included to illustrate the sign-up page, profile settings page, and admin page.

docs/docs/guidelines/login.mdx

@@ -20,6 +20,12 @@ The following environment variables are crucial in configuring the login setting
 - _`LANGFLOW_SECRET_KEY`_: A key used for encrypting the superuser's password.
 - _`LANGFLOW_NEW_USER_IS_ACTIVE`_: Determines whether new users are automatically activated. Default is `False`.
 
+All of these variables can be passed to the CLI command _`langflow run`_ through the _`--env-file`_ option. For example:
+
+```bash
+langflow run --env-file .env
+```
+
 <Admonition type="info">
   It is critical not to expose these environment variables in your code
   repository. Always set them securely in your deployment environment, for