Issue 798 - Auditing PFMERGE command docs

[Kannav02]

This PR aims to find and fix inconsistencies in the documentation for the PFMERGE command as mentioned in the issue #798

The objectives of this PR can be simplified in the points below

• Run the command and its examples in a local instance of DiceDB and make sure they work as per requirements
• Compare the command with Redis's counterpart and make sure that the results are the same
• In the official documentation, format the headings with the correct title as specified in the issue
• Remove the Conclusion heading if it exists
• Appropriate use of headers
• Convert Parameters and Return Value to a markdown table format to ensure consistency

end goal - documentation should match the format followed by SET and be consistent with how the code works

Fixes #798

[AshwinKul28]

HI @Kannav02 Thanks a lot for the changes, can you please add an error example (Invalid Usage) as well if possible?
Also please update the PR title.

[Kannav02]

sure i will update the PR title, also just to follow up ,
you've told in the issue to use Examples as the heading to display the examples for the CLI usage
but in the SET documentation, Example Usage is being utilised
should I still go ahead and make the change to Examples

thank you!

[Kannav02]

@AshwinKul28 ,I think the PR should be good for review now

Thank you!

[lucifercr07]

LGTM