adds architecture overview diagram (#2258)

website/content/docs/getting-started/index.mdx

@@ -8,6 +8,8 @@ description: Getting started with Boundary
 
 Before getting started with Boundary, it's important to understand a few key concepts. Please consult our [Boundary concepts](/docs/concepts) page to familiarize yourself with Boundary's architecture and terminology.
 
+![Boundary Architecture](/img/architecture-overview.png)
+
 ## Requirements
 
 The Getting Started section uses HCP Boundary, a HashiCorp hosted and fully-managed version of the Boundary product.

website/content/docs/oss/installing/index.mdx

@@ -10,3 +10,5 @@ description: |-
 This section covers installing Boundary for different modes of operation and across different environments
 
 For community-supported reference architectures, please see [Reference Architectures](/docs/oss/installing/reference-architectures).
+
+![Boundary Architecture](/img/architecture-overview.png)