Add comment about adding ':' characters into AAAA records read

from TinyDNS files

octodns/source/tinydns.py

@@ -47,6 +47,12 @@ class TinyDnsBaseSource(BaseSource):
         }
 
     def _data_for_AAAA(self, _type, records):
+        '''
+        TinyDNS files have the ipv6 address written in full, but with the
+        colons removed. This inserts a colon every 4th character to make
+        the address correct.
+        '''
+
         values = []
         for record in records:
             values.append(u":".join(textwrap.wrap(record[0], 4)))