Add module installation statements in Object detection demo file (#8626)

[jaykshirsagar05]

added installation statement of tf_slim module

Description

tf_slim installation statement was missing which was causing an error, updated the file to download this module.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist

• I have signed the Contributor License Agreement.
• I have read guidelines for pull request.
• My code follows the coding guidelines.
• I have performed a self code review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.

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