My First NFT Guide Update (#838)

* first draft of update, tested

* 3 intro fixes, thanks andrew

* Andrew fix

Thanks

Co-authored-by: Andrew Hariri <hariria@usc.edu>

* TS link more concise

Co-authored-by: Andrew Hariri <hariria@usc.edu>

* more fixes from andrew

* allow user to select operating system to see relevant terminal commands

* removed redundant Key Steps section

* found and cleaned up two .mdx links at the end

* removed extra callouts about saving files and instructions on how to create files

* Update apps/nextra/pages/en/build/guides/your-first-nft.mdx

Co-authored-by: Andrew Hariri <hariria@usc.edu>

* rm prerequisites

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Co-authored-by: Andrew Hariri <hariria@usc.edu>

Author: tippi-fifestarr