doc: replace overview with a diagram

doc/sphinx/reference/continuous-integration.md

@@ -5,19 +5,10 @@ pipeline.
 
 ## Overview
 
-There are a number of components to this story:
-- Mir builds
-- unit, integration, acceptance and performance tests
-  - including our [WayLand Conformance Suite - WLCS](https://github.com/canonical/wlcs)
-- sanitizer runs
-- ABI checks
-- coverage measurement
-- `.deb` package builds
-- downstream Snap builds
-- end-to-end testing across different hardware
-  - test procedures maintained within [mir-ci](https://github.com/canonical/mir-ci)
-    and [checkbox-mir](https://github.com/canonical/checkbox-mir)
-  - automations defined in a private repository, as it includes infrastructure credentials
+There are a number of components to this story, and a diagram might make for a good overview:
+
+```{mermaid} continuous-integration.mmd
+```
 
 These are run at different stages in the pipeline, balancing the time it takes to run and the
 breadth of testing. We'll discuss those in more detail below.

doc/sphinx/reference/continuous-integration.mmd

@@ -0,0 +1,16 @@
+flowchart TD
+    PR{{Pull Request}} --> Builds(<a href="#mir-builds"><u>Builds and tests</u></a>
+                                  <a href="#unit-tests"><u>unit</u></a>
+                                  <a href="#acceptance-tests"><u>acceptance</u></a>
+                                  <a href="#integration-tests"><u>integration</u></a>
+                                  <a href="#performance-tests"><u>performance</u></a>)
+    PR --> Snaps(<a href="#downstream-snap-builds"><u>Downstream snaps</u></a>)
+    PR --> ABI(<a href="#abi-checks"><u>ABI checks</u></a>)
+    PR --> Coverage(<a href="#coverage-measurement"><u>Coverage</u></a>)
+    Push{{Push}} --> Builds
+    Push --> Coverage
+    Push --> Sanitizers(<a href="#sanitizer-runs"><u>Sanitizers</u></a>)
+    Push --> PPA(<a href="#deb-package-builds"><u><tt>.deb</tt> packages</u></a>)
+    PPA --> Snaps
+    Snaps --> EndToEnd(<a href="#end-to-end-testing"><u>End-to-end testing</u></a>)
+