Add comment for ignore list

Author: Pierre-Sassoulas

script/check_changelog.py

@@ -22,6 +22,10 @@
 VALID_ISSUE_NUMBER_PATTERN: Pattern[str] = re.compile(r"\*[\S\s]*?#\d{1,5}")
 PATH_TO_WHATSNEW = (Path(__file__).parent / "../doc/whatsnew").resolve()
 UNCHECKED_VERSION = [
+    # Not checking version prior to 1.0.0 because the issues referenced are a mix
+    # between Logilab's internal and bitbucket. It's hard to tell, it's
+    # inaccessible for Logilab and often dead links for bitbucket anyway.
+    # Not very useful generally, unless you're an open source historian.
     "0",
 ]