How to download the documentation of a programming library for offline use.

1. On the documentation website, look for "downloads" section. Preferrably choose HTML format, because then it will be nicely searchable - I can even create a krunner web shortcut for searching it. Example: Numpy - find "HTML+zip".
2. If you need pytorch, torchvision, or sklearn - simply download https://github.com/unknownue/PyTorch.docs.
3. If you need the documentation hosted on https://readthedocs.io: in the bottom left press "Read the docs" a download type from "Downloads". Search field won't work in the HTML version, so feel free to download whatever format you like. Example: Elpy. Warning: for some libraries (e.g. more-itertools) the downloaded version is basically broken, so you should check if what you've downloaded is complete.
4. In some weird cases ReadTheDocs documentation for the latest version might of a library might be unlisted in the downloads secion of ReadTheDocs. For example, if you click the readthedocs icon in the bottom right of https://click.palletsprojects.com/en/master/, you won't find a download link for version 8.0. In this case copy the hyperlink https://media.readthedocs.org/pdf/pallets-click/latest/pallets-click.pdf or https://media.readthedocs.org/pdf/pallets-click/stable/pallets-click.pdf and replace pallets-click with the name of the project you want. It doesn't work for all projects, but it works for some.
5. Use httrack to mirror the documentation website. In my experience it doesn't take long. Do it like $ httrack https://click.palletsprojects.com/en/7.x/. This will download everything hosted in https://click.palletsprojects.com/en/7.x/ and will not go outside of this server directory. In this case the search field won't work.