bpo-41858: Clarify line in optparse doc (GH-22407)

The existing line is easily read as being incomplete.
diff --git a/Doc/library/optparse.rst b/Doc/library/optparse.rst
index c1a18e0..b109419 100644
--- a/Doc/library/optparse.rst
+++ b/Doc/library/optparse.rst
@@ -55,7 +55,7 @@
    <yourscript> -q -foutfile
    <yourscript> -qfoutfile
 
-Additionally, users can run one of  ::
+Additionally, users can run one of the following ::
 
    <yourscript> -h
    <yourscript> --help