Doc: interleave columns pandas compat (#15383)

Add a `pandas_compat` note to `DataFrame.interleave_columns`

Authors:
  - Ray Bell (https://github.com/raybellwaves)
  - GALI PREM SAGAR (https://github.com/galipremsagar)

Approvers:
  - Lawrence Mitchell (https://github.com/wence-)

URL: #15383

python/cudf/cudf/core/dataframe.py

@@ -7556,6 +7556,12 @@ def interleave_columns(self):
         Returns
         -------
         The interleaved columns as a single column
+
+        .. pandas-compat::
+            **DataFrame.interleave_columns**
+
+            This method does not exist in pandas but it can be run
+            as ``pd.Series(np.vstack(df.to_numpy()).reshape((-1,)))``.
         """
         if ("category" == self.dtypes).any():
             raise ValueError(