Update deprecation warning message

IPython/utils/signatures.py

@@ -5,7 +5,8 b' 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