Add string for "Open Feedbin"

Co-authored-by: Cathy Sarisky <42299862+cathysarisky@users.noreply.github.com>

Author: EvanHahn

ghost/i18n/locales/context.json

@@ -189,7 +189,7 @@
     "One hour ago": "Time a comment was placed",
     "One min ago": "Time since a comment was made",
     "Open AOL Mail": "Shown on signup and signin if your email is detected as AOL Mail",
-    "Open Feedbin": "",
+    "Open Feedbin": "Shown on signup and signin if your email is detected as Feedbin",
     "Open Gmail": "Shown on signup and signin if your email is detected as Gmail",
     "Open Hey": "Shown on signup and signin if your email is detected as Hey",
     "Open Mail.ru": "Shown on signup and signin if your email is detected as Mail.ru",