.add_watch() can accept empty tag

Use https://changedetection.io/CHANGELOG.txt as a nice default page to watch

changedetectionio/store.py

@@ -133,7 +133,7 @@ class ChangeDetectionStore:
                 self.add_watch(url='http://www.quotationspage.com/random.php', tag='test')
                 self.add_watch(url='https://news.ycombinator.com/', tag='Tech news')
                 self.add_watch(url='https://www.gov.uk/coronavirus', tag='Covid')
-                self.add_watch(url='https://changedetection.io', tag='Tech news')
+                self.add_watch(url='https://changedetection.io/CHANGELOG.txt')
 
         self.__data['version_tag'] = version_tag
 
@@ -329,7 +329,7 @@ class ChangeDetectionStore:
         self.needs_write = True
         return changes_removed
 
-    def add_watch(self, url, tag, extras=None):
+    def add_watch(self, url, tag="", extras=None):
         if extras is None:
             extras = {}