DOC add meaning of max_patches=None in _compute_n_patches (scikit-learn#25999)

Co-authored-by: Guillaume Lemaitre <g.lemaitre58@gmail.com>

Author: Ily83

sklearn/feature_extraction/image.py

@@ -261,9 +261,9 @@ def _compute_n_patches(i_h, i_w, p_h, p_w, max_patches=None):
     p_w : int
         The width of a patch
     max_patches : int or float, default=None
-        The maximum number of patches to extract. If max_patches is a float
+        The maximum number of patches to extract. If `max_patches` is a float
         between 0 and 1, it is taken to be a proportion of the total number
-        of patches.
+        of patches. If `max_patches` is None, all possible patches are extracted.
     """
     n_h = i_h - p_h + 1
     n_w = i_w - p_w + 1