[3.7] bpo-35054: Add more index entries for symbols. (GH-10064). (GH-10120)

(cherry picked from commit ddb961d2abe5d5fde76d85b21a77e4e91e0043ad)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
diff --git a/Doc/library/time.rst b/Doc/library/time.rst
index 56f972c..d76e089 100644
--- a/Doc/library/time.rst
+++ b/Doc/library/time.rst
@@ -369,6 +369,9 @@
       :pep:`475` for the rationale).
 
 
+.. index::
+   single: %; datetime format
+
 .. function:: strftime(format[, t])
 
    Convert a tuple or :class:`struct_time` representing a time as returned by
@@ -500,6 +503,9 @@
    it is 3.
 
 
+.. index::
+   single: %; datetime format
+
 .. function:: strptime(string[, format])
 
    Parse a string representing a time according to a format.  The return value