doc(adrs): add theming peer dependency ADR-001 (#1560)

Co-authored-by: George Treviranus <3946669+geotrev@users.noreply.github.com>

Author: jzempel

README.md

@@ -165,6 +165,7 @@ the links below to learn more.
 - Major release [migration](docs/migration.md) instructions
 - Component [API](docs/api.md)
 - [Development](docs/development.md) guidelines
+- Architectural [decision](docs/adrs/#readme) records
 
 ## Contribution
 

docs/adrs/001-theming-peer-dependency.md

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+# ADR-001: Theming peer dependency
+
+2023.04.24
+
+## Context
+
+Garden provides a collection of React components through multiple NPM packages.
+Each package has peer dependencies for `@zendeskgarden/react-theming`, `react`,
+`react-dom`, and `styled-components`. Typically, a package should increase its
+major version when there is a change in its peer dependency requirements.
+However, Garden proposes a DECISION to deviate from this [general
+rule](https://nodejs.org/en/blog/npm/peer-dependencies) and allow special
+treatment for `@zendeskgarden/react-theming`.
+
+While this decision conflicts with [semantic versioning](https://semver.org/),
+it benefits both maintainers and consumers by enabling a centralized, tested
+collection of hooks and utilities across the codebase. As a result, consumers
+are not required to ingest duplicated and more brittle code. A terminal warning
+will notify the consumer if a peer version is out-of-date.
+
+Ideally, all Garden package versions should align. However, at the very least,
+the `@zendeskgarden/react-theming` peer dependency should align with the highest
+version of a Garden component package dependency.
+
+## Decision
+
+As [centralized theming
+utilities](https://garden.zendesk.com/components/utilities) are added or
+modified (in non-breaking fashion), other Garden component packages may take
+advantage of them by updating their `@zendeskgarden/react-theming` peer dependency
+minor version without publishing a major version breaking change.
+
+## Consequences
+
+If a consumer upgrades a single Garden component package, they may see a console
+warning indicating that the `@zendeskgarden/react-theming` package is
+out-of-date. If the warning is ignored, there is a high likelihood that
+component rendering will fail due to a missing theming utility. However, there
+is no reason to believe that such a failure could slip through to production.

docs/adrs/README.md

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+# Architectural Decision Records
+
+Garden architectural decison records (ADRs) capture important decisions made,
+along with context and consequences.
+
+- [ADR-001](./001-theming-peer-dependency.md): Theming peer dependency