Install rails_admin and devise. Start setting it up.

app/views/devise/mailer/reset_password_instructions.html.erb

@@ -0,0 +1,8 @@
+<p>Hello <%= @resource.email %>!</p>
+
+<p>Someone has requested a link to change your password. You can do this through the link below.</p>
+
+<p><%= link_to 'Change my password', edit_password_url(@resource, reset_password_token: @token) %></p>
+
+<p>If you didn't request this, please ignore this email.</p>
+<p>Your password won't change until you access the link above and create a new one.</p>