Add missing hooked docs in content.php

[ribaricplusplus]

This is just a minor documentation fix, adding a missing @hooked entry.

The undocumented hooking that this PR adds happens here:

storefront/inc/storefront-template-hooks.php

Line 63 in 55376f5

add_action( 'storefront_loop_post', 'storefront_post_taxonomy', 40 );

Note: Build failing because this has not yet been pushed to wp-env: WordPress/gutenberg#29800

[ralucaStan]

Thank you @ribaricplusplus for adding the missing doc. I will approve your change.