gh-106318: Add example for str.count() (#134519)

Author: blaisep

Doc/library/stdtypes.rst

@@ -1805,8 +1805,18 @@ expression support in the :mod:`re` module).
    interpreted as in slice notation.
 
    If *sub* is empty, returns the number of empty strings between characters
-   which is the length of the string plus one.
-
+   which is the length of the string plus one. For example::
+
+      >>> 'spam, spam, spam'.count('spam')
+      3
+      >>> 'spam, spam, spam'.count('spam', 5)
+      2
+      >>> 'spam, spam, spam'.count('spam', 5, 10)
+      1
+      >>> 'spam, spam, spam'.count('eggs')
+      0
+      >>> 'spam, spam, spam'.count('')
+      17
 
 .. method:: str.encode(encoding="utf-8", errors="strict")