Add comments clarifying some things added here

Guido van Rossum · Guido van Rossum · commit 2c9250eb1827 · 2016-12-09T12:13:02.000-08:00
diff --git a/setup.cfg b/setup.cfg
@@ -21,6 +21,10 @@ parallel = true
 show_missing = true
 
 [metadata]
+# This seems to be used only by bdist_wheel.
+# You need "pip3 install wheel".
+# Then run "python3 setup.py bdist_wheel" to build a wheel file
+# (and then upload that to PyPI).
 requires-dist =
     typed-ast >= 0.6.1; sys_platform != 'win32'
     typing >= 3.5.2; python_version < "3.5"
diff --git a/setup.py b/setup.py
@@ -9,6 +9,9 @@
     sys.stderr.write("ERROR: You need Python 3.2 or later to use mypy.\n")
     exit(1)
 
+# This requires setuptools when building; setuptools is not needed
+# when installing from a wheel file (though it is still neeeded for
+# alternative forms of installing, as suggested by README.md).
 from setuptools import setup
 from setuptools.command.build_py import build_py
 from mypy.version import base_version
@@ -92,6 +95,10 @@ def run(self):
 if os.name == 'nt':
     scripts.append('scripts/mypy.bat')
 
+# These requirements are used when installing by other means than bdist_wheel.
+# E.g. "pip3 install ." or
+# "pip3 install git+git://github.com/python/mypy.git"
+# (as suggested by README.md).
 install_requires = []
 if sys.platform != 'win32':
     install_requires.append('typed-ast >= 0.6.1')
