docs: add missing period

Author: angeloashmore

README.md

@@ -9,7 +9,7 @@
 
 Helpers to integrate Prismic into Next.js apps.
 
-- 👁️  Set up Prismic previews
+- 👁️  Set up Prismic previews.
 - 🔗  Display Prismic images using [`next/image`][next-image].
 - 🖼️  Display Prismic links using [`next/link`][next-link].