Add draft user warning

Author: JamesParrott

Diff for: shapefile.py

@@ -14,7 +14,9 @@
 import os
 import sys
 import tempfile
+import textwrap
 import time
+import warnings
 import zipfile
 from datetime import date
 from struct import Struct, calcsize, error, pack, unpack
@@ -93,6 +95,27 @@
     from urllib2 import HTTPError, Request, urlopen
     from urlparse import urlparse, urlunparse
 
+if sys.version_info < (3, 9):
+    warnings.showwarning(
+        textwrap.dedent("""\
+        Warning!
+
+        The PyShp developers propose to drop support for Pythons 3.8 and earlier, including Python 2.
+        Thereafter, Python version support will follow the official Python release
+        cycle: https://devguide.python.org/versions/.  This will make Python 3.9 the earliest
+        supported version until October 2025.
+
+        The reasoning behind this is available in the following discussion:
+        https://github.com./GeospatialPython/pyshp/discussions/290
+        Please post any feedback there.
+
+        Many thanks,
+        """),
+        category=UserWarning,
+        filename=__name__,
+        lineno=99,
+    )
+
 
 # Helpers