Add a comment explaining subscribers count calculation

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

@@ -59,6 +59,9 @@ public class PeertubeAccountExtractor extends ChannelExtractor {
 
     @Override
     public long getSubscriberCount() throws ParsingException {
+        // The subscriber count cannot be retrieved directly. It needs to be calculated.
+        // An accounts subscriber count is the number of the channel owner's subscriptions
+        // plus the sum of all sub channels subscriptions.
         long subscribersCount = json.getLong("followersCount");
         String accountVideoChannelUrl = baseUrl + PeertubeChannelLinkHandlerFactory.API_ENDPOINT;
         if (getId().contains(ACCOUNTS)) {