Add French’s Gettext file, with very little translations

I do not know enough French to do the full translations, but i wanted to
make sure that it would work.

Makefile

@@ -2,7 +2,7 @@ HTML_FILES := $(shell find web -name *.gohtml)
 GO_FILES := $(shell find . -name *.go)
 DEFAULT_DOMAIN = camper
 POT_FILE = po/$(DEFAULT_DOMAIN).pot
-LINGUAS = ca es
+LINGUAS = ca es fr
 MO_FILES = $(patsubst %,locale/%/LC_MESSAGES/$(DEFAULT_DOMAIN).mo,$(LINGUAS))
 XGETTEXTFLAGS = --no-wrap --from-code=UTF-8 --package-name=camper --msgid-bugs-address=jordi@tandem.blog
 DEMO_SQL = demo.sql