docs: add account resource to domain model docs (#532)

website/content/docs/concepts/domain-model/accounts.mdx

@@ -0,0 +1,15 @@
+---
+layout: docs
+page_title: Domain Model - Action 
+sidebar_title: Action
+description: |-
+  The annatomy of a Boundary account 
+---
+
+# Action
+
+A Boundary account is a resource that contains the login name and password for the password authentication method. Accounts are not users, but can be associated with users. A login name is a not a username and vice versa. Accounts are a special case for the password auth method because other auth methods already store account information (such as OIDC).
+
+## Attributes
+
+Accounts contain a `login name` and a `password`.

website/data/docs-navigation.js

@@ -36,6 +36,7 @@ export default [
       {
         category: 'domain-model',
         content: [
+				  'accounts',
           'actions',
           'auth-methods',
           'grants',