Update deprecation warning message

IPython/utils/signatures.py

@@ -1,11 +1,12 b''
 """DEPRECATED: Function signature objects for callables.
 
 Use the standard library version if available, as it is more up to date.
 Fallback on backport otherwise.
 """
 
 import warnings
-warnings.warn("{} backport for Python 2 is deprecated in IPython 6, which only supports Python 3".format(__name__),
+warnings.warn("{} backport for Python 2 is deprecated in IPython 6, which only supports "
+              "Python 3. Import directly from  standard library `inspect`".format(__name__),
     DeprecationWarning, stacklevel=2)
 
 from inspect import BoundArguments, Parameter, Signature, signature