How do you describe the technologies and solutions implemented in the project?

Question

Documentation

Hello!
Tell me, how do you accompany the improvements, implementations and integrations of the project?
Example : integration was carried out, during which a number of technical nuances arose that need to be taken into account by those who will support the project in the future (even you, your team).
Task : so that when you later return to the integration for its refinement, development or troubleshooting by you or another developer, there is some kind of introductory, by which, roughly speaking, you can’t get past and without which the work will not be complete ( building crutches, overlooking important details ) .

Answer 1

README.md at the root of the repository - and you can't get past it. Well, if the project is on github, bitbucket etc.
//TODO: notice in specific places in the code. IDEs catch such tags and draw attention to themselves