Add friendlier and more accurate instructions in invitation email

Copy Example:

To accept the invitation:
  POST /accept-invitation username=<username>
    password=<password> email=you@domain.tld
    secret=8c6b5719-7b1c-471c-bdea-7807b6c0866c

1 files changed, 1 insertions, 1 deletions

diff --git a/src/App.hs b/src/App.hs
index d83f75e30265..e56e7c1875f5 100644
--- a/src/App.hs
+++ b/src/App.hs
@@ -69,7 +69,7 @@ sendInviteEmail T.Config{..} email@(T.Email to) (T.InvitationSecret secretUUID)
     subject = "You've been invited!"
     body =
       let secret = secretUUID |> UUID.toString in
-        cs configServer ++ "/accept-invitation?email=" ++ cs to ++ "&secret=" ++ secret
+        "To accept the invitation: POST /accept-invitation username=<username> password=<password> email=" ++ cs to ++ " secret=" ++ secret
 
 server :: T.Config -> Server API
 server config@T.Config{..} = createAccount