add service manual and project board info

README.md

@@ -8,3 +8,17 @@ NHS App Frontend is mainatined by staff at NHS England. If you have a question,
 
 - [#general](https://nhs-service-manual.slack.com/archives/CDJ29AQCD) on NHS service manual Slack
 - [#forum-app-design-system](https://nhsdigitalcorporate.enterprise.slack.com/archives/C06GY1LRP19) on NHS England Slack
+
+## Building on the NHS digital service manual
+
+The NHS App uses the [NHS design system](https://service-manual.nhs.uk/design-system), however it also uses many custom design styles, components and patterns that we need to document.
+
+## Documenting NHS App design styles, components and patterns
+
+We use a GitHub project board to document design styles, components and patterns being used on the NHS app, along with any work, including visual design changes, hypotheses, user insights etc. All this information then links back to the [NHS digital service manual community backlog](https://github.com/nhsuk/nhsuk-service-manual-community-backlog/projects/1) for others to learn from the work.
+
+---
+
+### **[View and discuss NHS App design styles, components and patterns](https://github.com/orgs/nhsuk/projects/8/views/1)**
+
+---