Added FAQ

FAQ.md

@@ -152,6 +152,7 @@ FairEmail follows all the best practices for an email client as decribed in [thi
 * [(88) How can I use a Yahoo! account?](#user-content-faq88)
 * [(89) How can I send plain text only messages?](#user-content-faq89)
 * [(90) Why are some texts linked while not being a link?](#user-content-faq90)
+* [(91) Can you add periodical synchronization to save battery power?](#user-content-faq91)
 
 [I have another question.](#support)
 
@@ -1476,6 +1477,14 @@ This is why texts are sometimes recognized as links, which is better than not re
 
 <br />
 
+<a name="faq91"></a>
+**(91) Can you add periodical synchronization to save battery power?**
+
+Synchronizing messages is an expensive proces because the local and remote messages need to be compared,
+so periodically synchronizing messages will not result in saving battery power, more likely the contrary.
+
+<br />
+
 
 ## Support