Pigo is a Go library for detecting faces by using the PICO algorithm. Compared to the Viola-Jones method, PICO is fast. Naturally, PIGO is fast too. Add this to the fact that GoCV uses cgo, which adds a penalty for speed, and PIGO may seem to be a better option overall. However, it must be noted that the PICO algorithm is more prone to false positives than the original Viola-Jones method.
Using the PIGO library is simple. The provided documentation is clear. However, PIGO was designed to run within the author's workflow. Differing from that workflow will require some tiny amount of extra work. Specifically, the author draws images using external helpers such as github.com/fogleman/gg. We shan't. However, the work isn't much.
To install pigo, simply run go get -u github.com/esimov/pigo/....