Add option to place fortune in a box

[nabaco]

Switched to Alpha from Startify, and I am missing the option to "boxify" the fortune quote, like so:

This is the vimscript code that does it in Startify:
https://github.com/mhinz/vim-startify/blob/4e089dffdad46f3f5593f34362d530e8fe823dcf/autoload/startify/fortune.vim#L8