tip: update package doc to refer to stable code
tip: update package doc to refer to stable code

This comment was written and has not been changed since this package was
created: https://www.youtube.com/watch?v=1rZ-JorHJEY

It is no longer called 'tipgodoc', and it is no longer all that 'new'. This
change request updates that text to reflect the current state of the 'tip'
command.

Change-Id: I4ce56fb9a3bd617cf92f8d53df5a2d4726085a9a
Reviewed-on: https://go-review.googlesource.com/24860
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

syreclabs/go-tools,golang/tools,golang/tools,golang/tools,golang/tools,syreclabs/go-tools,syreclabs/go-tools,syreclabs/go-tools,syreclabs/go-tools,golang/tools,syreclabs/go-tools