cli: add 'config init' command

my/core/preinit.py

@@ -0,0 +1,13 @@
+from pathlib import Path
+
+def get_mycfg_dir() -> Path:
+    import appdirs # type: ignore[import]
+    import os
+    # not sure if that's necessary, i.e. could rely on PYTHONPATH instead
+    # on the other hand, by using MY_CONFIG we are guaranteed to load it from the desired path?
+    mvar = os.environ.get('MY_CONFIG')
+    if mvar is not None:
+        mycfg_dir = Path(mvar)
+    else:
+        mycfg_dir = Path(appdirs.user_config_dir('my'))
+    return mycfg_dir