Document decision to use ADRs

Why these changes are being introduced:

We are about to make major architectural decisions about this
application, and we need a framework for recording them.

Relevant ticket(s):

* https://mitlibraries.atlassian.net/browse/GDT-123

How this addresses that need:

This adds an initial architectural decision record (ADR) to confirm
that we will use ADRs in this repo.

Side effects of this change:

Future significant architectural decisions should be documented
as ADRs.

doc/adr/0001-record-architecture-decisions.md

@@ -0,0 +1,19 @@
+# 1. Record architecture decisions
+
+Date: 2024-01-22
+
+## Status
+
+Accepted
+
+## Context
+
+We need to record the architectural decisions made on this project.
+
+## Decision
+
+We will use Architecture Decision Records, as [described by Michael Nygard](http://thinkrelevance.com/blog/2011/11/15/documenting-architecture-decisions).
+
+## Consequences
+
+See Michael Nygard's article, linked above. For a lightweight ADR toolset, see Nat Pryce's [adr-tools](https://github.com/npryce/adr-tools).