add readme

packages/identity-agent/README.md

@@ -1,5 +1,26 @@
+<!-- TODO: This is just a start. Will add a better description eventually. -->
+
 ## Description
 
-This package implements the building blocks in `@web5/agent` in order to provide a minimum implementation of an Identity Agent. 
+This package provides an implementation of a web5 agent using the building blocks in `@web5/agent`.
+
+While similar to `@web5/user-agent`, this package differs by not using IndexedDB for the DID Resolution Cache (detailed below). Use `@web5/user-agent` on web platforms with IndexedDB access. For platforms without IndexedDB access (e.g., React Native), this package is more suitable.
+
+## Implementation
+
+Start by examining the self-documenting [identity-agent.ts](./src/identity-agent.ts) file.
+
+#### DidResolver
+
+If you do not supply a `DidResolver`, the agent defaults to an unpersisted in-memory cache. For larger production applications, supply `create` with a custom `DidResolver` featuring a `cache` attribute, which should be a class implementing the `DidResolverCache` class.
+
+Browsers with IndexedDB access can utilize `DidResolverCacheLevel`. In such cases, using the `@web5/user-agent` package is recommended, as it employs this persistent cache by default.
+
+```typescript
+const didResolver = new DidResolver({
+  cache: new CustomDidResolverCache(),
+  didResolvers: [DidIonMethod, DidKeyMethod],
+});
 
-<!-- TODO: This is just a start. Will add a better description eventually. -->  
+IdentityAgent.create({ didResolver });
+```