Update password reset copy so as not to reveal whether the email exists

A malicious user could use this to test which email addresses are in the
user database.

bookwyrm/templates/landing/password_reset_request.html

@@ -9,7 +9,13 @@
         <div class="block">
             <h1 class="title">{% trans "Reset Password" %}</h1>
 
-            {% if message %}<p class="notification is-primary">{{ message }}</p>{% endif %}
+            {% if sent_message %}
+            <p class="notification is-primary">
+            {% blocktrans trimmed %}
+            A password reset link will be sent to <strong>{{ email }}</strong> if there is an account using that email address.
+            {% endblocktrans %}
+            </p>
+            {% endif %}
 
             <p>{% trans "A link to reset your password will be sent to your email address" %}</p>
             <form name="password-reset" method="post" action="/password-reset">