mcookie: add page

[nsuthison]

• The page (if new), does not already exist in the repo.
• The page is in the correct platform directory (common/, linux/, etc.)
• The page has 8 or fewer examples.
• The PR title conforms to the recommended templates.
• The page follows the content guidelines.
• The page description includes a link to documentation or a homepage (if applicable).

[tldr-bot]

The build for this PR has failed with the following error(s):

Error: Parse error on line 15:
...{{number_of_bytes}}`s`- Print the deti
-----------------------^
Expecting 'NEWLINE', 'TEXT', 'DASH', 'BACKTICK', got 'COMMAND_TEXT'
pages/linux/mcookie.md:14: TLDR103 Command example is missing its closing backtick

Please fix the error(s) and push again.

[sbrl]

Thanks for the new page, @name! I've left some comments below for you to review.