Clarify expectations in new language request email

The notification mail did not clearly state what is next expected step,
let's describe it explicitely.

Issue #783
Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/html/mail/new_language.html

@@ -11,6 +11,10 @@
 {% blocktrans %}there has been a request for new language on {{ translation }} at {{ site_title }}.{% endblocktrans %}
 </p>
 
+<p>
+{% trans "Please add the language file to VCS, Weblate will automatically discover it on next update." %}
+</p>
+
 <table>
 <tr>
 

weblate/html/mail/new_language.txt

@@ -2,6 +2,8 @@
 
 {% blocktrans %}there has been a request for new language on {{ translation }} at {{ site_title }}.{% endblocktrans %}
 
+{% trans "Please add the language file to VCS, Weblate will automatically discover it on next update." %}
+
 {% trans "Requested language:" %}
 
 {{ language.name }} ({{ language.code }})