docs: Move custom identity provider docs to READMEs.

docs/IDENTITIES.md

@@ -129,3 +129,42 @@ The resulting output is a JSON object containing the identity information:
   }
 }
 ```
+
+## Custom identity providers
+
+A custom identity provider can be used provided the module takes the following form:
+```javascript
+// A unique name for the identity provider
+const type = 'custom'
+
+// check whether the identity was signed by the identity's id.
+const verifyIdentity = identity => {
+
+}
+// The identity provider.
+const MyCustomIdentityProvider = ({ keystore }) => {
+  const getId = async ({ id } = {}) => {
+
+  }
+
+  const signIdentity = async (data, { id } = {}) => {
+
+  }
+
+  return {
+    getId,
+    signIdentity
+  }
+}
+
+export { MyCustomIdentityProvider as default, verifyIdentity, type }
+```
+
+To use it, add it to the list of known identity providers:
+
+```javascript
+import as MyCustomIdentityProvider from 'my-custom-identity-provider'
+addIdentityProvider(MyCustomIdentityProvider)
+```
+
+where my-custom-identity-provider is the custom module.

src/identities/providers/index.js

@@ -1,57 +1,13 @@
 /**
  * @module IdentityProviders
  * @description
- * Identity providers.
- *
- * ## Custom Providers
- *
- * An identity provider provides a method for signing and verifying an
- * identity using a particular cryptographic mechanism.
- *
- * A custom identity provider can be used provided the module takes the
- * following form:
- * ```javascript
- * // A unique name for the identity provider
- * const type = 'custom'
- *
- * // check whether the identity was signed by the identity's id.
- * const verifyIdentity = identity => {
- *
- * }
- *
- * // The identity provider.
- * const MyCustomIdentityProvider = ({ keystore }) => {
- *   const getId = async ({ id } = {}) => {
- *
- *   }
- *
- *   const signIdentity = async (data, { id } = {}) => {
- *
- *   }
- *
- *   return {
- *     getId,
- *     signIdentity
- *   }
- * }
- *
- * export { MyCustomIdentityProvider as default, verifyIdentity, type }
- * ```
- *
- * To use it, add it to the list of known identity providers:
- * ```javascript
- * import * as MyCustomIdentityProvider from 'my-custom-identity-provider'
- * addIdentityProvider(MyCustomIdentityProvider)
- * ```
- *
- * where my-custom-identity-provider is the custom module.
+ * Identity providers for signing and verifying an identity using various
+ * cryptographic mechanism.
  */
 import * as PublicKeyIdentityProvider from './publickey.js'
 
 const identityProviders = {
   publickey: PublicKeyIdentityProvider
-  // [DIDIdentityProvider.type]: DIDIdentityProvider,
-  // [EthIdentityProvider.type]: EthIdentityProvider
 }
 
 /**