Fingerprint description string corrected.

app/src/main/res/values/fingerprint_viewer.xml

 <?xml version="1.0" encoding="utf-8"?>
 <resources>
-    <string name="otr_fingerprint_description">Your opponent can provide his fingerprint you can compare with specified here to be sure he is who you think he is. You should not use XMPP chat for this purpose.</string>
+    <string name="otr_fingerprint_description">To confirm the identity of your opponent, ask him to provide his fingerprint and compare it with the one below. For this purpose, you should not exchange fingerprints by XMPP chat.</string>
     <string name="otr_is_verified">This contact is trusted</string>
     <string name="otr_local_fingerprint">Your fingerprint:</string>
     <string name="otr_remote_fingerprint">Your opponent\'s fingerprint:</string>