[DOC] add note to install pandoc

[inclinedadarsh]

Reference Issues/PRs

Fixes #2467

What does this implement/fix? Explain your changes.

Includes a note to install Pandoc

Does your contribution introduce a new dependency? If yes, which one?

No.

Any other comments?

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I have added the following labels to this PR based on the title: [ $\color{#F3B9F8}{\textsf{documentation}}$ ].

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[baraline]

Lgtm thanks !