USWDS-site: Replace nunjucks reference

[amyleadem]

Summary

Replaced Nunjucks reference with Twig

Related issue

Closes #2809

Preview link

Pagination page

Problem statement

Nunjucks is mentioned in pagination guidance and we no longer use it. We should replace with more general guidance or remove it completely.

Solution

Replaced "Nunjucks" references with "Twig" and added a link to the related source code.

Testing and review

• Confirm the copy update is appropriate and accurate
• Confirm the new link points to the correct location

[mahoneycm]

Lgtm! I see the related behaviors in the template found at the new link. I think this is likely a better place to point users than including comments they'll need to erase in source code.

[cathybaptista]

Just feedback. Not a blocker.

[cathybaptista]

Just a preference... I think there isn't a comma after "behaviors below" and before the "and" in this sentence: We've outlined these behaviors below, and included them in the Twig templates for Pagination in our source code. Other than that measly thing, LGTM!