Update README.md with info about running unit tests

Created new top level section 'Development', placed existing 'Continuous
Integration' and new 'Running Tests' sections in it. Reordered sections to
place 'Installation' ahead of 'Development'.

README.md

@@ -58,14 +58,6 @@ def my_fakefs_test(fs):
 Similar to the unittest class (`fake_filesystem_unittest.TestCase`), the `fs` fixture stubs
 out all file system functions and modules.
 
-## Continuous Integration
-
-pyfakefs is automatically tested with Python 2.6 and above, and it is currently
-[![Build Status](https://travis-ci.org/jmcgeheeiv/pyfakefs.svg)](https://travis-ci.org/jmcgeheeiv/pyfakefs).
-
-See [Travis-CI](http://travis-ci.org) for
-[test results for each Python version](https://travis-ci.org/jmcgeheeiv/pyfakefs).
-
 ## Installation
 
 ### Compatibility
@@ -78,6 +70,32 @@ pyfakefs works with [PyTest](doc.pytest.org) version 2.8.0 or above.
 ### PyPi
 [pyfakefs is available on PyPi](https://pypi.python.org/pypi/pyfakefs/).
 
+## Development
+
+### Continuous Integration
+
+pyfakefs is automatically tested with Python 2.6 and above, and it is currently
+[![Build Status](https://travis-ci.org/jmcgeheeiv/pyfakefs.svg)](https://travis-ci.org/jmcgeheeiv/pyfakefs).
+
+See [Travis-CI](http://travis-ci.org) for
+[test results for each Python version](https://travis-ci.org/jmcgeheeiv/pyfakefs).
+
+### Running Tests
+
+pyfakefs unit tests are available via two test scripts:
+
+```bash
+$ python all_tests.py
+$ py.test pytest_plugin_test.py
+```
+
+These scripts are called by `tox` and Travis-CI. `tox` can be used to run tests
+locally against supported python versions:
+
+```bash
+$ tox
+```
+
 ## History
 pyfakefs.py was initially developed at Google by Mike Bland as a modest fake
 implementation of core Python modules.  It was introduced to all of Google