Instructions on how to write a custom price fetcher

[alensiljak]

Hi! I'd like to add some sources that I'm using and would appreciate some guidance on how exactly should a custom price fetcher be implemented.
Other than the sources inside beanprice, I've seen that pricehist can also be used as an external source so I'll look at that implementation.
But this issue is mainly to collect the required information for those who want to implement additional price sources. I would submit a PR with addition to the readme once I understand what exactly is needed.

[alensiljak]

Working notes:

• Source is an interface to be implemented by all price sources.
• The source returns a SourcePrice.
• The required method(s):
  • get_latest_price()

[xuhcc]

The documentation page is https://docs.google.com/document/d/1thYRAMell_QT1Da1F_laprSs6BlROZjyK_h3V8qHW9c/edit

But it is not up to date.

[alensiljak]

Thank you! I will suggest an edit, to point to this repository.
I have a basic source working, with only get_latest_price, but am running into the async issue with cache. #91
I would summarize my findings once everything is ready and perhaps we can add it to the readme?

[xuhcc]

Instructions were added in #114