Doc: Add explanation of how migrations work

[VladimirRubin]

I just added some clarity on how migrations work under the hood to better understand the tool

[olso]

hey, we've found out the hard way, that https://github.com/rt2zz/redux-persist#state-reconciler also plays a big role

[VladimirRubin]

hey, we've found out the hard way, that https://github.com/rt2zz/redux-persist#state-reconciler also plays a big role

Could you please give more details?

[olso-nordsec]

hey, we've found out the hard way, that https://github.com/rt2zz/redux-persist#state-reconciler also plays a big role

Could you please give more details?

https://github.com/rt2zz/redux-persist/blob/master/docs/api.md#type-statereconciler