[Melilot Brandybuck]

Some time ago someone here at BD posted a link to an appendix written by JRRT where Gandalf and the hobbits are discussing the aftermath of their adventures. I believe Merry asks him what caused him to choose Bilbo to accompany the dwarves to Erebor and Gandalf goes on to explain some of the decisions he had to make leading up to their quest.

Could someone please tell me in which book this appendix can be found, and perhaps the link also?

Thank you.