DOC: recommend to turn on deprecation warnings for Python >= 2.7.

This was brought up on the mailing list on 10 Sep 2010.

README.txt

@@ -16,6 +16,12 @@ After installation, tests can be run with:
 
 python -c 'import numpy; numpy.test()'
 
+When installing a new version of numpy for the first time or before upgrading
+to a newer version, it is recommended to turn on deprecation warnings when
+running the tests:
+
+python -Wd -c 'import numpy; numpy.test()'
+
 The most current development version is always available from our
 git repository:
 

doc/TESTS.txt

@@ -41,6 +41,13 @@ follows::
   >>> import numpy
   >>> numpy.test()
 
+Note that for Python >= 2.7 deprecation warnings are silent by default. They
+can be turned on (recommended after installation and before upgrading) by
+starting the interpreter with the -Wd switch, or by::
+
+  >>> import warnings
+  >>> wwarnings.simplefilter('always', DeprecationWarning)
+
 The test method may take two or more arguments; the first is a string
 label specifying what should be tested and the second is an integer
 giving the level of output verbosity. See the docstring for numpy.test