docs(templates): fix grammar in README (#13027)

## Summary

Fixed a grammatical error in the README files for the website templates.

## Changes

- Fixed grammar in the on-demand revalidation section: changed "or
footer or header, change they will" to "footer, or header changes will"

## Files Changed

- `templates/website/README.md`
- `templates/with-vercel-website/README.md`

## Type of Change

- [x] Documentation fix/improvement
- [ ] Bug fix
- [ ] New feature
- [ ] Breaking change

This fixes a typo that was making the sentence grammatically incorrect
and hard to read.

Author: adamklingbaum

templates/website/README.md

@@ -142,7 +142,7 @@ In addition to draft previews you can also enable live preview to view your end
 
 ## On-demand Revalidation
 
-We've added hooks to collections and globals so that all of your pages, posts, or footer or header, change they will automatically be updated in the frontend via on-demand revalidation supported by Nextjs.
+We've added hooks to collections and globals so that all of your pages, posts, footer, or header changes will automatically be updated in the frontend via on-demand revalidation supported by Nextjs.
 
 > Note: if an image has been changed, for example it's been cropped, you will need to republish the page it's used on in order to be able to revalidate the Nextjs image cache.
 

templates/with-vercel-website/README.md

@@ -166,7 +166,7 @@ In addition to draft previews you can also enable live preview to view your end
 
 ## On-demand Revalidation
 
-We've added hooks to collections and globals so that all of your pages, posts, or footer or header, change they will automatically be updated in the frontend via on-demand revalidation supported by Nextjs.
+We've added hooks to collections and globals so that all of your pages, posts, footer, or header changes will automatically be updated in the frontend via on-demand revalidation supported by Nextjs.
 
 > Note: if an image has been changed, for example it's been cropped, you will need to republish the page it's used on in order to be able to revalidate the Nextjs image cache.