Document where to place static data

[abitrolly]

https://vuejs.org/api/options-state.html mentions this.$data` property, which is used to hold reactive data. Holding large JSON lists there probably gives a performance penalty even if the data is not changed and only accessed.

It would be nice to document this "static data" vs "reactive data" in Vue, as well as indicate the best approach to store static data.

Based on vuejs/core#8749