add command to update po file in Makefile

doc/Makefile

@@ -7,4 +7,5 @@
 SPHINXBUILD   ?= sphinx-build
 SOURCEDIR     = .
 BUILDDIR      = _build
+LANGUAGE      ?= en
 
@@ -10,7 +11,7 @@
 
-LANGUAGE ?= en
+.PHONY: help Makefile gettext update_locale clean
 
 # Put it first so that "make" without argument is like "make help".
 help:
 	@$(SPHINXBUILD) -M help "$(SOURCEDIR)" "$(BUILDDIR)/$(LANGUAGE)$(BUILDDIRSUFFIX)" $(SPHINXOPTS) $(O)
 
@@ -12,10 +13,11 @@
 
 # Put it first so that "make" without argument is like "make help".
 help:
 	@$(SPHINXBUILD) -M help "$(SOURCEDIR)" "$(BUILDDIR)/$(LANGUAGE)$(BUILDDIRSUFFIX)" $(SPHINXOPTS) $(O)
 
-.PHONY: help Makefile gettext
+clean:
+	rm -rf $(BUILDDIR)/*
 
 gettext: Makefile
 	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)$(BUILDDIRSUFFIX)" $(SPHINXOPTS) $(O)
 
@@ -18,7 +20,11 @@
 
 gettext: Makefile
 	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)$(BUILDDIRSUFFIX)" $(SPHINXOPTS) $(O)
 
+# used to update *.po files
+update_locale: Makefile gettext
+	@sphinx-intl update -p "$(BUILDDIR)$(BUILDDIRSUFFIX)/gettext" -l fr
+
 # Catch-all target: route all unknown targets to Sphinx using the new
 # "make mode" option.  $(O) is meant as a shortcut for $(SPHINXOPTS).
 %: Makefile