add missing translation string to fix broken translation

Author: corwintines

src/intl/en/common.json

@@ -138,6 +138,7 @@
   "page-developers-aria-label": "Developers' Menu",
   "page-index-meta-title": "Home",
   "page-last-updated": "Page last updated",
+  "page-what-is-ethereum-what-is-ether": "What is ether?",
   "pbs": "Proposer-builder separation",
   "pools": "Pooled staking",
   "privacy-policy": "Privacy policy",