Update readme to clarify when store updates a component

[reins-ch]

After troubleshooting for a long time and not understanding why my component was not rerendered when the state changed, I read through the code.
It turns out getRenderingRef of @stencil/core only returns truthy when it is currently in a render function.
And the result of getRenderingRef is used to mark if a component should be rerendered:

stencil-store/src/subscriptions/stencil.ts

Line 36 in 1701999

if (elm) {

So I just want to save anyone else the time and trouble of finding this by just clarifying it in the readme.

[beenotung]

So it only trigger auto re-rendering when you access the store in the "render" method, not other place like constructor and "connectedCallback" method?

[Serabe]

@beenotung exactly. If we take a look at the component's lifecycle, the part in pink is the rerender process:

Anything in the constructor, connectedCallback or similar methods outside the pink circle won't be run in the rerender so it makes no sense to rerender anything because a property only accessed there changed.

[beenotung]

That makes sense. Store is used to hold shared state for the purpose of rending (and re-rendering).

Thanks for the clarification.