The snail package is a MetaPost module within the ConTeXt LMTX environment, designed for creating flowcharts and similar procedural graphics.

Assuming you have properly installed the ConTeXt LMTX environment following the installation instructions on the ConTeXt wiki, and that your ConTeXt LMTX installation directory is /opt/context, proceed with the installation as follows:

$ git clone https://github.com/liyanrui/snail
$ cd snail
$ SNAILPATH=/opt/context/tex/texmf-local/tex/context/third/snail
$ mkdir -p $SNAILPATH
$ cp t-snail.mkxl $SNAIPATH
$ context --generate

An English guide is available in doc directory. It's the snail-tutorial.pdf file.

There also is a Chinese guide is available at https://zhuanlan.zhihu.com/p/1938871262509273817