Write the full URL or use an (inline) footnote.
The URL needs wrapped it in <>, so that it's interpreted correctly on all platforms.
A footnote may contain additional text.
you can download it at <https://bitcoincore.org/>... Bitcoin Core^[<https://bitcoincore.org/>]... Bitcoin Core^[Download at <https://bitcoincore.org/>]
To refer to a chapter use @sec:label, e.g. as explained in chapter @sec:schnorr.
If a chapter doesn't have a label yet, add {#sec:label} after its title, e.g. ## Schnorr Signatures {#sec:schnorr}.