What does this PR do?

Improve repo

For resources

Description

Added a small definition about programming/coding playgrounds for making it understandable to beginners

Why is this valuable (or not)?

Copy the definition merged in #6822 into the rest of CONTRIBUTING files, opening a 3 weeks window to translate it by our comunity

Checklist:

• Read our [contribu

Sanity checks

• My issue relates to a specific CLI completion spec (e.g. git checkout is missing options in git completion spec). If your issue is more general, please create your issue here: withfig/fig
• I have searched [github.com/withfig/autocomplete/issues](https://gi

importaddress (and possibly other legacy-only wallet functions), when used on a descriptor wallet, return a fairly nondescript error:

$ ./bitcoin-cli -regtest importaddress test
error code: -4
error message:
This type of wallet does not support this command

The RPC help of importaddress doesn't mention nor further explain this incompatibility, nor what alternative to use inste