improve the README

Author: antocuni

README.rst

@@ -18,11 +18,26 @@ PyPy:
 
 - PyPy3.6 7.1.1
 
+Live example
+-------------
+
+`pypy-manylinux-demo`_ is an example project which demonstrate how to build
+CPython and PyPy wheels using Travis CI and this image. It is a fork of the
+official `python-manylinux-demo`, and shows that building wheels for PyPy is
+as easy as changing the image name!
+
+.. _`pypy-manylinux-demo`: https://github.com/pypy/pypy-manylinux-demo
+.. _`python-manylinux-demo`: https://github.com/pypa/python-manylinux-demo
+
+How to run PyPy
+----------------
+
 The various PyPy versions are installed inside ``/opt/pypy/``, and they are
 also symlinked to ``/opt/python``. Moreover, each installation of PyPy
-contains also a ``python`` symlink; all the following commands are equivalent
-and run the PyPy interpreter, you can use whatever fits best in your build
-system:
+contains also a ``python`` symlink.
+
+All the following commands are equivalent and run the PyPy 2.7, version
+7.1.1. You can use whatever fits best in your build system:
 
 - ``/opt/pypy/pypy2.7-7.1.1/bin/pypy``
 
@@ -31,3 +46,29 @@ system:
 - ``/opt/python/pp271-pypy_41/bin/pypy``
 
 - ``/opt/python/pp271-pypy_41/bin/python``
+
+Similarly, these are the commands to run PyPy 3.6, version 7.1.1:
+
+- ``/opt/pypy/pypy3.6-7.1.1/bin/pypy``
+
+- ``/opt/pypy/pypy3.6-7.1.1/bin/python``
+
+- ``/opt/python/pp371-pypy3_71/bin/pypy``
+
+- ``/opt/python/pp371-pypy3_71/bin/python``
+
+
+PEP 425 Compatibility tags
+---------------------------
+
+``pp271-pypy_41`` and ``pp371-pypy3_71`` are the `PEP 425`_ compliant
+compatibility tag. In particular:
+
+- ``pp`` stands for PyPy (as opposed to ``cp`` which is CPython)
+
+- ``271`` and ``371`` mean "Python [2|3]", "PyPy 7.1.x".
+
+- ``pypy_41`` and ``pypy3_71`` are the binary ABI tags for the relevant
+  version of PyPy. You can probably ignore them.
+
+.. _`PEP 425`: https://www.python.org/dev/peps/pep-0425/