docs: make FEATURE_FLAGS.md reference a link (#16415)
docs: make FEATURE_FLAGS.md reference a link (#16415)


zhouyao1994/incubator-superset,apache/incubator-superset,airbnb/caravel,apache/incubator-superset,airbnb/caravel,airbnb/caravel,apache/incubator-superset,zhouyao1994/incubator-superset,apache/incubator-superset,zhouyao1994/incubator-superset,zhouyao1994/incubator-superset,airbnb/caravel,zhouyao1994/incubator-superset,apache/incubator-superset