Mention std/enumerate by name

[omentic]

Certainly on me, but I couldn't figure out how to import this module. Also conforms to what other std modules do.

[ghost]

Well, I feel like this is a bit of a "workaround" since std is not exclusive to the enumerate module only, std can be used for any stdlib modules.

[timotheecour]

this is not the 1st time this comes up, the fix is instead:

• fixing docgen as mentioned in No link to std/exitprocs in docs (+enumerate,jsonutils etc) #16046 (comment) to show for each module the import syntax
• extending spellsuggest (fix #2844 #3911; add --spellsuggest to suggest symbols in scope with similar spellings on undefined symbol error #16067) as described there:

make this flag also suggest when a module import is misspellt, including things like import exitprocs instead of import std/exitprocs

[omentic]

Closing in favor of #16046. Showing the import syntax would be great, even if it's only in the examples.