Update comment documentation of "site" attribute.

pretext/project/__init__.py

@@ -924,7 +924,7 @@ def validate_path(cls, path: t.Union[Path, str]) -> Path:
     publication: Path = pxml.attr(default=Path("publication"))
     # A path, relative to the project directory, prepended to any target's `output_dir`.
     output_dir: Path = pxml.attr(name="output-dir", default=Path("output"))
-    # A path prepended to any target's `site`.
+    # A path to the directory holding a project's landing page(s).
     site: Path = pxml.attr(default=Path("site"))
     # A path to stage files for deployment
     stage: Path = pxml.attr(default=Path("output/stage"))