Create //playbooks

I'm particularly excited about this idea. As I was reading Graham's "Erase your
darlings" blog post, I had an idea: I should have playbooks at the root of my
monorepo.

I can have playbooks for the following:
- How to install NixOS
- How to build GCR images from Nix expressions
- A collection of miscellaneous shell commands (e.g. "how to kill a process by name")
- What series of steps should I follow when I receive a paycheck

I already keep README's at the root of each package, which I think is where many
of these instructions belong. Other tutorials that I write for myself that do
not belong to any package can go in //playbooks. I also will host my personal
habits in //playbooks since habits are a bit like playbooks for life. Let's see
how this idea ages as the caffeine wears off...

playbooks/finances.org

@@ -0,0 +1,9 @@
+# Let's pretend it's April 1st; all amount go in the March (not April) column.
+* Finance Chain (25th of each month)
+** Open "finances_2020" Google Sheet
+** Settle up with Mimi on TransferWise
+** Adjust "Stocks (after tax)" to reflect amount Google sent
+** Add remaining cash to "Carryover (cash)"
+** Adjust "Paycheck" to reflect amount Google sent
+** In the "International Xfer" table, send "Xfer amount" from Monzo to USAA
+** Go to an ATM and extract the amount in "ATM withdrawal"