Add env-based site configuration

.env.local.example

@@ -0,0 +1,8 @@
+# Copy this file to `.env.local` and adjust values.
+# All vars prefixed with NEXT_PUBLIC_ are exposed to the browser.
+
+NEXT_PUBLIC_SITE_NAME="Your Name"
+NEXT_PUBLIC_SITE_TITLE="Your Personal Site"
+NEXT_PUBLIC_SITE_DESCRIPTION="Personal homepage and blog."
+NEXT_PUBLIC_SITE_URL="https://example.com"
+NEXT_PUBLIC_SITE_AUTHOR="Your Name"