feat: Add legend to proposal, preamble

Author: ADubhlaoich

documentation/proposals/DOP-001.md

@@ -15,10 +15,32 @@ This proposal describes my observations about the NGINX App Protect WAF document
 
 It will be shared with stakeholders to challenge or verify certain assumptions and to give the affected teams advance warning, as the changes involved are substantial.
 
+For clarity, here is a legend for the diagrams:
+
+```mermaid
+---
+title: Diagram legend
+---
+graph
+ section[Section]
+ page>Page]
+ usecase([Use case])
+```
+
+- A _section_ is a grouping of pages
+- A _page_ is a single document, made up of one or more use cases
+- A _use case_ is a set of instructions for a specific topic
+
+Understanding the relationship between pages and use cases is crticially important to contextualise the impact of how certain pages are currently structured.
+
 ## Issues identified
 
 ### Content duplication
 
+At the highest level, there is a gigantic amount of duplication from [the landing page](https://docs.nginx.com/nginx-app-protect-waf) to account for the V4/V5 split.
+
+To emphasize this duplication, I have illustrated the high level sections, which are identical.
+
 ```mermaid
 ---
 title: NGINX App Protect WAF folders
@@ -61,7 +83,7 @@ graph LR
     v5 --> 5rel
 ```
 
-At initial glance, this does not seem overly complex aside from the V4/5 split. Most of the content in the respective sections are identical, outside of deployment and v5-specific features.
+At initial glance, this does not seem overly complex outside of deployment and v5-specific features.
 
 As it stands, the majority of NAP documentation between the V4 and V5 branches are identical - they have the same pages and same sections. 
 
@@ -71,7 +93,9 @@ I think the structure reflects an earlier intent for V5/X to completely replace/
 
 As a result, humongous amounts of the content is replicated, which lead an over-use of includes.
 
-Each "step" through these folders is an additional user interaction when navigating through the sidebar. Focusing on a v4 diagram which includes include the individual pages illustrates some of the highest level differences, as well as the single page folder pattern we avoid.
+Each "step" through these folders is an additional user interaction when navigating through the sidebar. 
+
+Focusing on a v4 diagram which includes include the individual pages illustrates some of the highest level differences, as well as the single page folder pattern we avoid in other product documentation.
 
 ```mermaid
 ---
@@ -435,7 +459,7 @@ flowchart LR
  
 ```
 
-The documentation related to NGINX App Protect WAF currently stored within the NGINX Ingress Controller documentation set would be migrated to instead be managed and stored within the NGINX App Protect WAF documentation. TheV4/V5 split that created the current state of the documentation's IA was also inherited by NGINX Ingress Controller. 
+The documentation related to NGINX App Protect WAF currently stored within the NGINX Ingress Controller documentation set would be migrated to instead be managed and stored within the NGINX App Protect WAF documentation. The V4/V5 split that created the current state of the documentation's IA was also inherited by NGINX Ingress Controller. 
 
 
 ### Move Troubleshooting information into contextual pages