Add doc about translation using poedit (#6600)
Add doc about translation using poedit (#6600)

* Update CONTRIBUTING.md
mistercrunch/panoramix,airbnb/superset,zhouyao1994/incubator-superset,mistercrunch/panoramix,zhouyao1994/incubator-superset,apache/incubator-superset,airbnb/superset,zhouyao1994/incubator-superset,airbnb/caravel,airbnb/superset,zhouyao1994/incubator-superset,apache/incubator-superset,zhouyao1994/incubator-superset,apache/incubator-superset,apache/incubator-superset,mistercrunch/panoramix,airbnb/superset,mistercrunch/panoramix,apache/incubator-superset,airbnb/caravel,airbnb/caravel,airbnb/caravel