docs: update auxiliary programs

Now includes usage output, (hopefully) generated by the tool during the docs build process so it will always be up to date.
Included in makefile as `docs/usage` target.
Also some updates/additions to the description text, esp `yosys-filterlib` and `yosys-smtbmc`.

Makefile

@@ -969,7 +969,7 @@ docs/source/cmd/abc.rst: $(TARGETS) $(EXTRA_TARGETS)
 	mkdir -p docs/source/cmd
 	./$(PROGRAM_PREFIX)yosys -p 'help -write-rst-command-reference-manual'
 
-PHONY: docs/gen_images docs/guidelines
+PHONY: docs/gen_images docs/guidelines docs/usage
 docs/gen_images:
 	$(Q) $(MAKE) -C docs/source/_images all
 
@@ -978,8 +978,15 @@ docs/guidelines:
 	$(Q) mkdir -p docs/source/temp
 	$(Q) cp -f $(addprefix guidelines/,$(DOCS_GUIDELINE_FILES)) docs/source/temp
 
+# many of these will return an error which can be safely ignored, so we prefix
+# the command with a '-'
+DOCS_USAGE_PROGS := yosys-config yosys-filterlib yosys-abc yosys-smtbmc yosys-witness
+docs/usage: $(addprefix docs/source/temp/,$(DOCS_USAGE_PROGS))
+docs/source/temp/%: docs/guidelines
+	-$(Q) ./$(PROGRAM_PREFIX)$* --help > $@ 2>&1
+
 DOC_TARGET ?= html
-docs: docs/source/cmd/abc.rst docs/gen_images docs/guidelines
+docs: docs/source/cmd/abc.rst docs/gen_images docs/guidelines docs/usage
 	$(Q) $(MAKE) -C docs $(DOC_TARGET)
 
 clean: