'wheels only' warning

See discussion on gh-8

README.rst

@@ -42,6 +42,13 @@ To install a package locally for development, run::
 
     flit install [--symlink]
 
+.. note::
+
+   Flit only creates packages in the new 'wheel' format. People using older
+   versions of pip (<1.5) or easy_install will not be able to install them.
+   People may also want a traditional sdist for other reasons, such as Linux
+   distro packaging. I hope that these problems will diminsh over time.
+
 Flit packages a single importable module or package at a time, using the import
 name as the name on PyPI. All subpackages and data files within a package are
 included automatically.