Improve Contributing section in readme

[riQQ]

This makes it more obvious that the API key needs to be provided when using Tangram Play. See also the instructions provided at #87 (comment).

[ENT8R]

Thank you for your proposal!

While I think that the addition to the readme makes perfectly sense, I don't really think that it is necessary to add another hint in the style files as there is already a hint where all constants/global variables are defined:

streetcomplete-mapstyle/global.yaml

Lines 1 to 2 in 59fbc4d

	global:
	api_key: false # intended to be overwritten by StreetComplete

After all, the website at https://streetcomplete.github.io/streetcomplete-mapstyle/ offers more or less the same functionality to edit a style (via the pencil icon in the top left corner) even without requiring to use an API key.

Was it difficult for you to figure out how to edit the styles?

[riQQ]

It took my a while to figure it out for Tangram Play.

I only discovered the link to https://streetcomplete.github.io/streetcomplete-mapstyle/, after I already setup Tangram Play with the API key. Maybe this should be the prefered way of editing for the Contributing section in the readme with an annotation that it doesn't need an API key for jawg.io.

What do you think about that?

[ENT8R]

Your suggestion sounds great! Would you like to modify this PR to implement this suggestion?
I'm sorry I didn't respond earlier, but as the Jawg style is not the only map style, I also wanted to offer a solution to link to the other map styles. I did this now with dafd6d1, so the different styles can be directly linked:

https://streetcomplete.github.io/streetcomplete-mapstyle/?provider=jawg&style=light
https://streetcomplete.github.io/streetcomplete-mapstyle/?provider=jawg&style=dark
https://streetcomplete.github.io/streetcomplete-mapstyle/?provider=jawg&style=satellite

[riQQ]

@ENT8R updated the PR. Can you take another look, please?

[riQQ]

@ENT8R thanks for catching the error and the suggested improvement. I implemented your suggestions.

[ENT8R]

Sorry, I somehow forgot about this PR, thank you for bringing it back to my attention