This image is based on the popular Alpine Linux project, available in the alpine official image. Alpine Linux is much smaller than most distribution base images (~5MB), and thus leads to much slimmer images in general.
This variant is highly experimental, and not officially supported by the Go project (see golang/go#19938 for details).
The main caveat to note is that it does use musl libc instead of glibc and friends, which can lead to unexpected behavior. See this Hacker News comment thread for more discussion of the issues that might arise and some pro/con comparisons of using Alpine-based images.
To minimize image size, additional related tools (such as git, gcc, or bash) are not included in Alpine-based images. Using this image as a base, add the things you need in your own Dockerfile (see the alpine image description for examples of how to install packages if you are unfamiliar). See also docker-library/golang#250 (comment) for a longer explanation.