add release notes for v2, v3

RELEASE_NOTES.md

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+# Release Notes
+
+## v3 — 2026-07-16
+
+- Added a favicon (clock + "H" mark), with a transparent icon set for
+  browser tabs and an opaque apple-touch-icon for iOS.
+- New customer form now redirects to the customer list after saving,
+  instead of the new customer's edit page.
+- Customer addresses in the customer list now link out to a Google Maps
+  search (URL-encoded, opens in a new tab).
+
+## v2 — 2026-07-16
+
+- Added a "+ New Customer" button and a standalone `/customers/new`
+  form, so a customer's contact info can be added without first
+  creating a service order. Reuses the edit-customer template for both
+  create and edit.