Update the list of elaboration shell commands
Update the list of elaboration shell commands

Cover all and only the commands understood by |parseElabShellStep|,
defined in ParseShell.hs.

The previous list omitted some commands and included others that no longer
were available.

Also:

- Groups the commands (general, view proof state, alter proof state)
- Adds an intro summarizing how interactive proving works at a high level.
- Advises the reader to pull in the `Language.Reflection.Elab` module
  _before_ entering the elaboration shell.

markuspf/Idris-dev,enolan/Idris-dev,adnelson/Idris-dev,aaronc/Idris-dev,tpsinnem/Idris-dev,jeremy-w/Idris-dev,mpkh/Idris-dev,KaneTW/Idris-dev,mrmonday/Idris-dev,shlevy/Idris-dev,jeremy-w/Idris-dev,uuhan/Idris-dev,ozgurakgun/Idris-dev,adnelson/Idris-dev,Heather/Idris-dev,tpsinnem/Idris-dev,adnelson/Idris-dev,TimRichter/Idris-dev,Heather/Idris-dev,TimRichter/Idris-dev,TimRichter/Idris-dev,mrmonday/Idris-dev,uuhan/Idris-dev,tpsinnem/Idris-dev,Heather/Idris-dev,kojiromike/Idris-dev,markuspf/Idris-dev,markuspf/Idris-dev,aaronc/Idris-dev,enolan/Idris-dev,ben-schulz/Idris-dev,lenary/Idris-dev,bravit/Idris-dev,jmitchell/Idris-dev,jeremy-w/Idris-dev,KaneTW/Idris-dev,aaronc/Idris-dev,ozgurakgun/Idris-dev,markuspf/Idris-dev,ozgurakgun/Idris-dev,KaneTW/Idris-dev,bravit/Idris-dev,bravit/Idris-dev,uuhan/Idris-dev,FranklinChen/Idris-dev,KaneTW/Idris-dev,ben-schulz/Idris-dev,tpsinnem/Idris-dev,markuspf/Idris-dev,shlevy/Idris-dev,adnelson/Idris-dev,mrmonday/Idris-dev,markuspf/Idris-dev,eklavya/Idris-dev,jeremy-w/Idris-dev,adnelson/Idris-dev,ben-schulz/Idris-dev,aaronc/Idris-dev,bravit/Idris-dev,aaronc/Idris-dev,mpkh/Idris-dev,lenary/Idris-dev,eklavya/Idris-dev,shlevy/Idris-dev,lenary/Idris-dev,aaronc/Idris-dev,eklavya/Idris-dev,kojiromike/Idris-dev,mrmonday/Idris-dev,lenary/Idris-dev,FranklinChen/Idris-dev,jeremy-w/Idris-dev,lenary/Idris-dev,TimRichter/Idris-dev,ben-schulz/Idris-dev,enolan/Idris-dev,enolan/Idris-dev,TimRichter/Idris-dev,jmitchell/Idris-dev,ben-schulz/Idris-dev,uuhan/Idris-dev,TimRichter/Idris-dev,adnelson/Idris-dev,FranklinChen/Idris-dev,FranklinChen/Idris-dev,uuhan/Idris-dev,Heather/Idris-dev,eklavya/Idris-dev,eklavya/Idris-dev,uuhan/Idris-dev,tpsinnem/Idris-dev,Heather/Idris-dev,jmitchell/Idris-dev,jmitchell/Idris-dev,uuhan/Idris-dev,kojiromike/Idris-dev,shlevy/Idris-dev,jmitchell/Idris-dev,tpsinnem/Idris-dev,bravit/Idris-dev,ozgurakgun/Idris-dev,FranklinChen/Idris-dev,ozgurakgun/Idris-dev,mpkh/Idris-dev,bravit/Idris-dev,KaneTW/Idris-dev,mrmonday/Idris-dev,mrmonday/Idris-dev,mpkh/Idris-dev,kojiromike/Idris-dev,jeremy-w/Idris-dev,shlevy/Idris-dev,enolan/Idris-dev,kojiromike/Idris-dev,mpkh/Idris-dev,lenary/Idris-dev,KaneTW/Idris-dev,shlevy/Idris-dev,Heather/Idris-dev,ben-schulz/Idris-dev,kojiromike/Idris-dev,jmitchell/Idris-dev,eklavya/Idris-dev,ozgurakgun/Idris-dev,mpkh/Idris-dev,FranklinChen/Idris-dev,markuspf/Idris-dev,enolan/Idris-dev