Added query function [skip ci]

examples/query_function.py

@@ -0,0 +1,21 @@
+""" example function for osxphotos --query-function """
+
+
+from typing import List
+
+from osxphotos import PhotoInfo
+
+
+# call this with --query-function:examples/query_function.py::best_selfies
+def best_selfies(photos: List[PhotoInfo]) -> List[PhotoInfo]:
+    """your query function should take a list of PhotoInfo objects and return a list of PhotoInfo objects (or empty list)"""
+    # this example finds your best selfie for every year
+
+    # get list of selfies sorted by date
+    photos = sorted([p for p in photos if p.selfie], key=lambda p: p.date)
+
+    start_year = photos[0].date.year
+    stop_year = photos[-1].date.year
+    print(start_year, stop_year)
+
+    return photos