avoid warning, as we always pass HTML fragment

"/usr/lib/python3/dist-packages/feed2toot/message.py:48: MarkupResemblesLocatorWarning: The input looks more like a filename than markup. You may want to open this file and pass the filehandle into Beautiful Soup.
  finaltweet = BeautifulSoup(finaltweet, 'html.parser').get_text()"
See rationale at https://bugs.launchpad.net/beautifulsoup/+bug/2052988

feed2toot/main.py

@@ -25,7 +25,8 @@ import sys
 import re
 
 # external liraries imports
-from bs4 import BeautifulSoup
+import warnings
+from bs4 import BeautifulSoup, MarkupResemblesLocatorWarning
 
 # app libraries imports
 from feed2toot.addtags import AddTags
@@ -68,6 +69,8 @@ class Main:
 
     def main(self):
         '''The main function'''
+        warnings.filterwarnings("ignore", category=MarkupResemblesLocatorWarning)
+
         clip = CliParse()
         clioptions = clip.options
         self.setup_logging(clioptions)