DOC: Fix doc for DataFrame.plot subplots argument (#50599)

Fix doc for DataFrame.plot subplots argument

`.. versionadded` was missing a newline between it and the previous paragraph, and so wasn't being rendered.

Author: otaithleigh

Diff for: pandas/plotting/_core.py

@@ -662,6 +662,7 @@ class PlotAccessor(PandasObject):
           create 2 subplots: one with columns 'a' and 'c', and one
           with columns 'b' and 'd'. Remaining columns that aren't specified
           will be plotted in additional subplots (one per column).
+
           .. versionadded:: 1.5.0
 
     sharex : bool, default True if ax is None else False