The note is added to the Lone Wanderer's Pip-Boy after reading the "#000" entry on the first Museum Information terminal, located on the southern wall of the first floor of the Museum of Technology Atrium.
Hey there Jiggs,
I finally found a good place to ditch your share of the loot. It was hell getting here, but I made it. I left the usual breadcrumbs all over some of the info terminals in this place; their computer security was a joke. Complete the sequence and you're home free, but make any mistakes and the system will lock you out. We'll meet up in the usual spot later.