Clarify syntax for linguist-generated attribute

[HaraldNordgren]

Spell out syntax for marking files as generated in .gitattributes.

Why:

Clearing up confusion about to turn on and turn off linguist-generated.

What's being changed (if available, include any code snippets, screenshots, or gifs):

Updating docs. Related discussions: 99designs/gqlgen#3763

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• The changes in this PR meet the docs fundamentals that are required for all content.
• All CI checks are passing and the changes look good in the review environment.

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[lildude]

👍 from a Linguist perspective (I don't believe I have final say so don't take my approval as the final say). This is now inline with setting and unsetting as per the .gitattributes docs and also now inline with the Linguist docs.

[Sharra-writes]

@HaraldNordgren Thanks for opening a PR! I'm guessing you're right about this one, but I'm checking in with the repositories team to make sure.

[lildude]

@HaraldNordgren Thanks for opening a PR! I'm guessing you're right about this one, but I'm checking in with the repositories team to make sure.

It is. You can ping me in Slack if you need any further clarification or confirmation.

[Sharra-writes]

@lildude @HaraldNordgren Works for me! I'll get this approved and added to the merge queue.

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