[peertube] add feed url in channels

extractor/src/main/java/org/schabi/newpipe/extractor/services/peertube/extractors/PeertubeChannelExtractor.java

@@ -57,7 +57,7 @@ public class PeertubeChannelExtractor extends ChannelExtractor {
 
     @Override
     public String getFeedUrl() throws ParsingException {
-        return null;
+        return getBaseUrl() + "/feeds/videos.xml?accountId=" + json.get("id");
     }
 
     @Override