Add note about txt vs rst extension for docs (#1239)

src/snowflake/cli/app/dev/docs/generator.py

@@ -78,6 +78,9 @@ def _render_usage(
             arguments.append(param)
         else:
             options.append(param)
+
+    # RST files are presumed to be standalone pages in the docs with a matching item in the left nav.
+    # Included files, which these are, need to use the .txt extension.
     file_path = root / f"usage-{command_name}.txt"
     log.info("Creating %s", file_path)
     with file_path.open("w+") as fh: