[docs] kv api example contract

[iamveritas]

adding kv api example contract

[halsaphi]

A comment to explain the magic numbers in the getters would be useful:

i.e.

string get_last_name() const {
return get<1>(this->last_name);
}

[halsaphi]

• comment on 'using' and 'action_wrapper' - explain why you use aliasing and the benefit of action_wrapper.

• is it possible to highlight differences in using kv api vs db api?

[iamveritas]

• comment on 'using' and 'action_wrapper' - explain why you use aliasing and the benefit of action_wrapper.
• is it possible to highlight differences in using kv api vs db api?

these are good thoughts but they are out of scope of this code example
for first one we have documentation to cover it, if user doesn't know what an action wrapper is s/he will look it up and find it.
for second it will be explained in the explainer page