PEP 660: add links to prototypes (GH-1998)

pep-0660.rst

@@ -1,5 +1,5 @@
 PEP: 660
-Title: Editable installs for pyproject.toml based builds
+Title: Editable installs for pyproject.toml based builds (wheel based)
 Author: Daniel Holth <dholth@gmail.com>, Stéphane Bidoul <stephane.bidoul@gmail.com>
 Sponsor: Paul Moore <p.f.moore@gmail.com>
 Discussions-To: https://discuss.python.org/t/draft-pep-editable-installs-for-pep-517-style-build-backends/8510
@@ -79,8 +79,8 @@ encouraged to document such potential differences.
 The Mechanism
 =============
 
-This PEP adds a single optional hook to the PEP 517 backend interface. The hook
-is used to build a wheel that, when installed, allows that distribution to be
+This PEP adds two optional hooks to the PEP 517 backend interface. These hooks
+are used to build a wheel that, when installed, allows that distribution to be
 imported from its source folder. 
 
 build_wheel_for_editable
@@ -202,6 +202,26 @@ With regard to the wheel ``.data`` directory, this PEP focuses on making the
 ``console_scripts``, make their ``scripts`` tiny wrappers around library
 functionality, or manage these from the source checkout during development.
 
+Prototypes
+==========
+
+At the time of writing this PEP, several prototype implementations are
+available in various frontends and backends. We provide links below to
+illustrate possible approaches.
+
+Frontends:
+
+- pip (`pull request <https://github.com/pypa/pip/pull/8212>`__)
+
+Build backends:
+
+- enscons (`pull request 1 <https://github.com/dholth/enscons/pull/9>`__,
+  `pull request 2 <https://github.com/dholth/enscons/pull/21>`__)
+- flit (`pull request <https://github.com/takluyver/flit/pull/400>`__)
+- hatchling (`sdist <https://pypi.org/project/hatchling/#files>`__)
+- pdm (`pull request <https://github.com/pdm-project/pdm-pep517/pull/36>`__)
+- setuptools (`setuptools_pep660 repository <https://github.com/dholth/setuptools_pep660>`_)
+
 Rejected ideas
 ==============