(PROPOSAL) 2-layers cache Documentation

[tonidas]

I think that the documentation should talk about the two layers of cache that the gem provides:

1. The memory cache layer
2. The custom cache layer

It's very confusing at first, because there is two TTLs, the one related to the memory cache layer (native) and the one related to the custom cache layer (optional).

I can do that if the contributors agree that this is relevant.

Cheers

[spk]

Yes sure if you think it need improvement pull request are welcome @tonidas cheers

[spk]

There is more information on the PR linked; feel free to submit a PR if its still not clear

[simshanith]

To clarify, the "custom" cache is used to cache the HTTP response from Open Exchange Rates. The other store is an "Exchange Rates Store" with interface defined by the Money gem, as mentioned in several spots in the docs.

https://github.com/RubyMoney/money#exchange-rate-stores

This distinction is important in understanding why both are necessary - they cache different things with different interfaces