At the moment the only up-to-date documentation maintained by the current NodeMCU team is in English and hosted at https://nodemcu.readthedocs.io/. It is part of the source code repository (/docs subfolder), kept in sync with the code and built & published automatically.

Changes to the NodeMCU project are made through Pull Requests (PRs) into the project's repository. A list of the completed PRs is here. You may click through each PR to read the associated detail, comments and commits.

A very high-level change log can be deduced from the tag/release descriptions.