Adopt ADRs (architectural decision records)

Adds the first ADR to the MinervaNeue skin.
The file is placed in a top-level `/adr` folder since the `/doc` folder
is already used for auto-generated documentation.

Change-Id: I83ad4a1bf8e81caaea9312d4c3efc3bf5ce419be

adr/0001-adopt-adrs.md

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+# 1. Adopt ADRs (Architectural decision records)
+
+Date: 2024-01-29
+
+## Status
+
+Accepted.
+
+Options:
+- Proposed - If a decision is still pending acceptance.
+- Accepted - If a decision has been accepted by the maintaining team.
+- Deprecated - If a decision is no longer relevant.
+- Superseded - If a decision has been replaced with a newer one. Should include
+  link to the newer ADR.
+
+## Context
+
+As the code and teams maintaining this repository change over time, the
+knowledge of why certain decisions were made in the past may be lost or poorly
+understood. In order to help future maintainers of this repository (as well as
+our future selves) make sense of this code, we need to keep records of any
+significant, atypical or otherwise notable decisions.
+
+Since architectural decisions are made gradually, these records should be easily
+editable and added incrementally as changes arise.
+
+## Decision
+
+We will adopt architecture decision records. This file serves as a template for
+ADRs. ADRs will be numbered markdown files placed in the /adr directory.
+The format will follow the Michael Nygard ARD style as described on the
+following web page:
+
+https://cognitect.com/blog/2011/11/15/documenting-architecture-decisions.html
+
+More guidance on how to write ADRS:
+https://adr.github.io/
+
+## Consequences
+
+When any important, atypical or otherwise notable decision is made within this
+codebase, an ADR should be created and placed inside this directory. It is up to
+the person with the most context to create the ADR with regards to that decision.
+The ADR should be brief and may link to Phabricator or other places that hold
+more context around the decision.
+
+ADRs may also be used to propose changes by framing the ADR as a proposal and
+marking the status as "proposed". If there is agreement to adopt the ADR, it's
+status should be change to "accepted".
+
+ADRs can also be marked "deprecated" or "superseded".
+
+