org: minor tweaks

* doc/org/ltlfilt.org: Update example.
* doc/org/ioltl.org: Explain %s briefly.

doc/org/ioltl.org

@@ -207,7 +207,8 @@ from tool to tool:
 | [[file:ltlfilt.org][=ltlgrind=]] | output formula | input filename | input line        | leading text | trailing text |
 
 Other =%=-sequences are supported by these tools, and documented in
-the output of =--help=.
+the output of =--help=.  For instance =%s= can be used to compute the
+size of a formula.
 
 By default everything is output to standard output, so that you can
 redirect the output to a file, and pipe it to another tool.  The

doc/org/ltlfilt.org

@@ -470,6 +470,9 @@ ltlfilt --help | sed -n '/The FORMAT/,/^$/p' | sed '$d'
                              Boolean subformulas count as 1)
   %f                         the formula (in the selected syntax)
   %F                         the name of the input file
+  %h, %[vw]h                 the class of the formula is the Manna-Pnueli
+                             hierarchy ([v] replaces abbreviations by class
+                             names, [w] for all compatible classes)
   %L                         the original line number in the input file
   %s                         the length (or size) of the formula
 #+end_example