[DOCS]Update Smart Classroom index content

[wiwaszko-intel]

Description

Updating the overview of Smart Classroom to include application flow.
Based on changes in:
#1463

Checklist:

• [ X ] I agree to use the APACHE-2.0 license for my code changes.
• [ X ] I have not introduced any 3rd party components incompatible with APACHE-2.0.
• [ X ] I have not included any company confidential information, trade secret, password or security token.
• [ X ] I have performed a self-review of my code.