Revert "PEP 518: Remove wheel from the example requirements since it's a dependency of setuptools"

This reverts commit df0126e.

Author: jeanas

source/specifications/declaring-build-dependencies.rst

@@ -34,7 +34,7 @@ An example ``build-system`` table for a project built with
 
    [build-system]
    # Minimum requirements for the build system to execute.
-   requires = ["setuptools"]
+   requires = ["setuptools", "wheel"]
 
 Build tools are expected to use the example configuration file above as
 their default semantics when a ``pyproject.toml`` file is not present.