Add a short summary of Stack, why Stack, and how to take Stack on Zoom

Especially as we are now all increasingly online, this includes a guide
on best practices for how to run a meeting online using Stack.

I'm uncertain of where best to link to it (index? individual local
pages?), but this should at least be linkable once up.

stack.md

@@ -0,0 +1,77 @@
+---
+layout: page
+title: Progressive Stack
+permalink: /stack/
+---
+# Stack
+
+Many TWC chapter meetings using a technique called [Progressive
+Stack](https://en.wikipedia.org/wiki/Progressive_stack) to manage the order of
+who speaks during a discussion. Below is a brief summary of why and how it
+works.
+
+## Principles
+
+Stack is intended to make group discussions more equitable to prevent a small
+group from dominating a discussion. A person, the _stack-taker_, manages the
+stack and is in charge of deciding the order of who speaks next. In particular,
+
+- Prefer to hear first from people who haven't spoken yet, or don't often
+  speak.
+- Prefer to hear first from marginalized people who may otherwise be silenced,
+  ignored, or discouraged by "they who shout loudest" or "first come first
+  served" orderings.
+
+Relatedly, registering a desire to speak should be a low-friction one-time
+action. For example, briefly raising a hand and attracting the attention of the
+stack-taker, rather than needing to hold a hand up until the current speaker
+has finished, which may not be possible for some people.
+
+In addition to a facilitator and minute-taker, we recommend having a third
+person to manage the stack.
+
+## In-person
+
+For in-person meetings, a person registers their desire to speak by raising a
+hand. If they want to interject or talk about a current point, they can raise
+both hands. When someone finishes speaking, the stack-taker chooses the next
+person to speak, returning to the facilitator if the stack is empty.
+
+## Remote meetings
+
+Taking stack has challenges in remote meetings, as not every participant will
+have video, it's hard to keep track of everyone's videos at once, and so on.
+Below are some procedures and tips we've found helpful managing the stack for
+specific remote meeting tools.
+
+### Zoom
+
+A person can "raise a hand" by:
+
+- Raising their hand if they are on video. This is not possible for people
+  without video, and may be infeasible for large meetings.
+- Using the `Raise Hand` feature in Zoom.
+    - NOTE: Meeting hosts cannot use the `Raise Hand` feature, so will have to
+      use some other mechanism to raise their hand.
+- Using one of the 👏 or 👍 emoji overlays.
+- Posting in the chat that they would like to speak.
+
+The person taking stack should then post changes to the stack in the chat. For example,
+
+```
+*person A raises hand*
+
+stack-taker: "stack: A"
+
+*person B raises hand*
+
+stack-taker: "stack: A, B"
+
+*person A talks*
+
+stack-taker: "stack: B"
+
+*person B talks*
+
+stack-taker: "stack:"
+```