DOC: Add missing parameter documentation to carpet plot function

Add missing parameter documentation to carpet plot function.

Avoid using ``None`` as the default value for the font size parameter,
and set it to the default value that is effectively used in the function
body.

Author: jhlegarreta

nireports/reportlets/nuisance.py

@@ -239,7 +239,7 @@ def plot_carpet(
     sort_rows="ward",
     drop_trs=0,
     legend=True,
-    fontsize=None,
+    fontsize=24,
 ):
     """
     Plot an image representation of voxel intensities across time.
@@ -278,7 +278,14 @@ def plot_carpet(
         :obj:`scipy.cluster.hierarchy.linkage`.
         Any other value that Python evaluates to ``True`` will use the
         default clustering, which is :obj:`sklearn.cluster.ward_tree`.
-
+    drop_trs: :obj:`int`, optional
+        Number of initial timepoints ("dummy scans"”" / non–steady-state volumes)
+        to ignore at the beginning of a timeseries when computing display
+        scaling and potentially other plot-derived stats.
+    legend : :obj:`bool`, optional
+        ``True`` to plot the legend.
+    fontsize : :obj:`int`, optional
+        Font size.
     """
     if segments is None:
         segments = {"whole brain (voxels)": list(range(data.shape[0]))}
@@ -346,8 +353,6 @@ def plot_carpet(
         ax.get_xaxis().set_visible(False)
         ax.get_yaxis().set_visible(False)
 
-    fontsize = fontsize or 24
-
     # Length before decimation
     n_trs = data.shape[-1]