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What makes a good README
Say what the project does in one line, then show how to install it and the smallest example that works. Readers decide in seconds whether a project fits, so features and requirements come next, followed by settings, development commands, how to contribute and the license. Sections you leave empty are left out.
Changelogs people can read
The changelog follows Keep a Changelog: newest release first, each with a date and its changes grouped as Added, Changed, Deprecated, Removed, Fixed and Security. Keep an Unreleased section at the top for changes that haven't shipped yet. With a repository address, each version links to the comparison with the one before.
Questions
Can I start from my commit history?
Yes. Paste git log --oneline output under From commit messages. Commits written as feat:, fix:, perf: and so on are sorted into the right groups, and breaking changes marked with ! are labelled. Edit the wording afterwards; commit messages are written for developers, changelogs for users.
Does it add the license text?
It adds a License section that names the license and points to a LICENSE file. Put the full license text in that file; the license's official page has it.
Where do the files go?
Download saves README.md or CHANGELOG.md to your device. Put it at the top level of your repository and code hosts will show it on the project page.