Fix the docstrings of the capitalize method.

Objects/bytes_methods.c

@@ -332,7 +332,8 @@ _Py_bytes_title(char *result, char *s, Py_ssize_t len)
 PyDoc_STRVAR_shared(_Py_capitalize__doc__,
 "B.capitalize() -> copy of B\n\
 \n\
-Return a copy of B with only its first character capitalized (ASCII).");
+Return a copy of B with only its first character capitalized (ASCII)\n\
+and the rest lower-cased.");
 
 void
 _Py_bytes_capitalize(char *result, char *s, Py_ssize_t len)

Objects/unicodeobject.c

@@ -6705,7 +6705,7 @@ PyDoc_STRVAR(capitalize__doc__,
              "S.capitalize() -> str\n\
 \n\
 Return a capitalized version of S, i.e. make the first character\n\
-have upper case.");
+have upper case and the rest lower case.");
 
 static PyObject*
 unicode_capitalize(PyUnicodeObject *self)