GH-38528: [Python][Compute] Improve strptime format description

Splits a long sentence, makes the language more directive.

Co-authored-by: Rok Mihevc <rok@mihevc.org>

python/pyarrow/_compute.pyx

@@ -1682,8 +1682,8 @@ class StrptimeOptions(_StrptimeOptions):
     ----------
     format : str
         Pattern for parsing input strings as timestamps, such as "%Y/%m/%d".
-        Note that the semantics of the format follow the C/C++ strptime, not the Python one:
-        there can be slight differences in behavior, for example, how the "%y" placeholder
+        Note that the semantics of the format follow the C/C++ strptime, not the Python one.
+        There are differences in behavior, for example how the "%y" placeholder
         handles years with less than four digits.
     unit : str
         Timestamp unit of the output.