Add basic README with developer mode overview.

Documents the package as a library consumed by a host Bedrock app, the
`initialize()` entry point, and a Developer Mode section (marked planned)
linking to the spec.

Author: djscruggs

README.md

@@ -1 +1,44 @@
-# bedrock-vue-wallet
+# bedrock-vue-wallet
+
+Vue 3 + Quasar UI components for a Bedrock-based digital credential wallet.
+Stores and shares [Verifiable Credentials][] and drives credential exchanges
+(OID4VCI, OID4VP, and CHAPI).
+
+## Usage
+
+This package is a **library**, not a runnable application. It is published as
+`@bedrock/vue-wallet` and consumed by a host Bedrock web app, which provides the
+backend (sessions, KMS, credential store) and the peer dependencies listed in
+`package.json` (`vue`, `vue-router`, `@bedrock/quasar`, `@bedrock/web-wallet`,
+etc.).
+
+The host app wires the wallet in via the `initialize()` export:
+
+```js
+import {initialize} from '@bedrock/vue-wallet';
+
+await initialize({app, router /*, features, quasarOptions */});
+```
+
+## Developer Mode (planned)
+
+> Status: **specified, not yet implemented.** See
+> [`docs/dev-mode-spec.md`](./docs/dev-mode-spec.md).
+
+A developer-only UI overlay for desktop development, where camera hardware and
+live issuers / relying parties are unavailable. It lets a developer drive wallet
+flows by hand instead of scanning QR codes and running real exchanges.
+
+- **Enable:** set a truthy `localStorage` flag `wallet.devMode` (e.g. in
+  DevTools: `localStorage.setItem('wallet.devMode', '1')`). Off by default; the
+  trigger is never installed in normal use, so production behavior is unchanged.
+- **Open the panel:** press backtick (`` ` ``) three times in quick succession.
+- **Tools:**
+  - **Paste exchange URL** — paste an `https:` (`iuv=1`),
+    `openid-credential-offer:`, or `openid4vp:` URL instead of scanning a QR
+    code; it is fed into the existing scanner exchange pipeline.
+  - **Seed test credentials** — once logged in, populate the dashboard with
+    synthetic credentials so credential display/management UIs can be developed
+    without running a full exchange.
+
+[Verifiable Credentials]: https://www.w3.org/TR/vc-data-model-2.0/