documentation of builtins

[bstarynk]

Note: I am not familiar with Twitter. If you want to contact me, send an email to basile@starynkevitch.net. I am also novice in rust and forking mican as an exercise in rust programming.

It would be nice if the builtins had some documentation, even in the README.md
I suggest for example:

Built-in Commands

• cd dir - to change working directory to dir
• pwd - to print current working directory

I don't understand why there is no exit builtin (and probably some ulimit one)

In particular, I cannot guess what is syar doing.