Suggest (doc) instead of all-bindings

[sogaiu]

This PR is an attempt to address the point made in this comment.

The suggested change in this PR is to mention (doc) instead of all-bindings in the text. Two positive points about this are:

1. Currently, use of all-bindings (with parens) may lead to truncated results in a default janet installation:

   $ janet
   Janet 1.37.1-fa75a395 linux/x64/gcc - '(doc)' for help
   repl:1:> (all-bindings)
   @[% %= * ... yield zero? zipcoll]
   

   In contrast, (doc) gives nicer grouped output that isn't truncated and this seems more suitable for the situation in question.

2. The surrounding parens for the (doc) option might make it more likely that a newcomer might meet success sooner compared to all-bindings (which one might forget or neglect to put the parens around if one were to follow the current text literally without much thought).

[pepe]

LGTM