Add some comments

src/harmless.py

@@ -1,6 +1,7 @@
 from . import abstract
 
 class HarmlessParser(abstract.AbstractParser):
+    """ This is the parser for filetypes that do not contain metadata. """
     mimetypes = {'application/xml', 'text/plain', 'application/rdf+xml'}
 
     def __init__(self, filename: str):

src/images.py

@@ -32,6 +32,9 @@ class PNGParser(abstract.AbstractParser):
         return True
 
 class GdkPixbufAbstractParser(abstract.AbstractParser):
+    """ GdkPixbuf can handle a lot of surfaces, so we're rending images on it,
+        this has the side-effect of removing metadata completely.
+    """
     def get_meta(self):
         out = subprocess.check_output(['exiftool', '-json', self.filename])
         meta = json.loads(out.decode('utf-8'))[0]

src/parser_factory.py

@@ -8,6 +8,7 @@ from typing import Type, TypeVar
 
 T = TypeVar('T', bound='abstract.AbstractParser')
 
+# This loads every parser in a dynamic way
 for module_loader, name, ispkg in pkgutil.walk_packages('.src'):
     if not name.startswith('src.'):
         continue