Added a warning about editing the files

Author: ESultanik

docs/extending_polyfile.md

@@ -143,7 +143,7 @@ def parse_example(file_stream, match):
 
 ### Kaitai Struct Parsers
 
-The majority of PolyFile’s parsers are automatically generated from the [Kaitai Struct format gallery](https://formats.kaitai.io/). They are compiled at build-time (in [`setup.py`](../setup.py)) to produce the pure-Python parsers in [`polyfile/kaitai/parsers/*.py`](../polyfile/kaitai/parsers/).
+The majority of PolyFile’s parsers are automatically generated from the [Kaitai Struct format gallery](https://formats.kaitai.io/). They are compiled at build-time (in [`setup.py`](../setup.py)) to produce the pure-Python parsers in [`polyfile/kaitai/parsers/*.py`](../polyfile/kaitai/parsers/). These parsers should not be edited since they are automatically generated and will be overwritten the next time PolyFile is rebuilt.
 
 Unfortunately, the Kaitai Struct parsers are not currently tagged based upon the MIME type of the files they parse. Therefore, PolyFile maintains a manual mapping from MIME types to Kaitai parsers. This mapping lives in [`polyfile.kaitaimatcher.KAITAI_MIME_MAPPING`](../polyfile/kaitaimatcher.py):
 ```python

polyfile/kaitai/parsers/README.md

@@ -0,0 +1,3 @@
+# Auto-Generated Parsers
+
+The parsers in this directory are automatically generated from the [Kaitai Struct format gallery](https://formats.kaitai.io/). They are rebuilt every time PolyFile is installed or packaged, and therefore **THESE FILES SHOULD NOT BE EDITED**.