add autocompletion

[eliranmal]

references

• http://www.linuxjournal.com/content/more-using-bash-complete-command
• http://tldp.org/LDP/abs/html/tabexpansion.html
• https://www.gnu.org/software/bash/manual/html_node/Programmable-Completion.html

libraries

• https://github.com/scop/bash-completion (used by yarn)