PEP 715: clarify what [package.tool] is (#3873)

Author: brettcannon

peps/pep-0751.rst

@@ -547,15 +547,21 @@ other is disallowed.
 ------------------
 
 - Optional
-- Same usage as that of the equivalent table from the
-  `pyproject.toml specification`_.
+- Table
+- Similar usage as that of the ``[tool]`` table from the
+  `pyproject.toml specification`_ , but at the package version level instead of
+  at the lock file level (which is also available via ``[tool]``).
+- Useful for scoping package version/release details (e.g., recording signing
+  identities to then use to verify package integrity separately from where the
+  package is hosted, prototyping future extensions to this file format, etc.).
 
 
 ``[tool]``
 ==========
 
 - Optional
-- Same usage as that of the equivalent table from the
+- Table
+- Same usage as that of the equivalent ``[tool]`` table from the
   `pyproject.toml specification`_.