invitation emails

app/mailers/invitation_mailer.rb

@@ -0,0 +1,12 @@
+class InvitationMailer < ApplicationMailer
+  def invite(user)
+    @user = user
+    @invitation_url = invitation_url(@user.invitation_token)
+    @expires_at = @user.invitation_sent_at + User::INVITATION_TOKEN_EXPIRY
+
+    mail(
+      to: @user.email,
+      subject: "You've been invited to join Sanasto Wiki"
+    )
+  end
+end