Update homepage and links in RegistrationStep4 component

package.json

@@ -2,7 +2,7 @@
   "name": "frontend",
   "version": "0.1.0",
   "private": true,
-  "homepage": "/membership",
+  "homepage": "/become-a-member",
   "dependencies": {
     "@fontsource/dm-sans": "^5.2.8",
     "@fontsource/fraunces": "^5.2.9",