Adding documentation, and altering timestamp to "local" timezone.

Author: Jason Smith

elements/rh-datetime/README.md

@@ -65,6 +65,10 @@ You can use any locale here.
 
 The value of this should be the same timestamp that you add to the light DOM.
 
+### timestamp (observed)
+
+A unix timestamp that will be converted for use in displaying the appropriate date. You would not use both datetime and timestamp, and the last updated will take precedence.
+
 ### type (observed)
 
 The options for type are:

elements/rh-datetime/src/rh-datetime.js

@@ -64,7 +64,10 @@ class RhDatetime extends RHElement {
 
     this._timestamp = val;
 
-    this.setDate(new Date(val * 1000));
+    /* Get local timezone offset */
+    let offset = new Date().getTimezoneOffset() * 60 * 1000;
+
+    this.setDate(new Date(val * 1000 + offset));
   }
 
   get datetime() {