DOC: Add wide_to_long to release notes.

Author: jseabold

doc/source/v0.13.0.txt

@@ -615,6 +615,23 @@ Enhancements
     ser = Series([1, 3, np.nan, np.nan, np.nan, 11])
     ser.interpolate(limit=2)
 
+- Added ``wide_to_long`` panel data convenience function.
+
+  .. ipython:: python
+
+    import pandas as pd
+    import numpy as np
+    np.random.seed(123)
+    df = pd.DataFrame({"A1970" : {0 : "a", 1 : "b", 2 : "c"},
+                       "A1980" : {0 : "d", 1 : "e", 2 : "f"},
+                       "B1970" : {0 : 2.5, 1 : 1.2, 2 : .7},
+                       "B1980" : {0 : 3.2, 1 : 1.3, 2 : .1},
+                       "X"     : dict(zip(range(3), np.random.randn(3)))
+                      })
+    df["id"] = df.index
+    df
+    wide_to_long(df, ["A", "B"], i="id", j="year")
+
 .. _scipy: http://www.scipy.org
 .. _documentation: http://docs.scipy.org/doc/scipy/reference/interpolate.html#univariate-interpolation
 .. _guide: http://docs.scipy.org/doc/scipy/reference/tutorial/interpolate.html