add whats new

docs/source/whatsnew/pr/autoformatting.rst

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+Code autoformatting
+===================
+
+The IPython terminal can now auto format your code just before entering a new
+line or executing a command. To do so use the
+``--TerminalInteractiveShell.autoformatter`` option and set it to ``'black'``;
+if black is installed IPython will use black to format your code when possible. 
+
+IPython cannot always properly format your code; in particular it will
+auto formatting with *black* will only work if:
+
+   - Your code does not contains magics or special python syntax. 
+
+   - There is no code after your cursor. 
+
+The Black API is also still in motion; so this may not work with all versions of
+black. 
+
+It should be possible to register custom reformatter, though the API is till in
+flux. 
+
+
+
+