Add warning explaining modules with no coverage

sevanspowell · sevanspowell · commit 3820af5b059c · 2022-07-15T12:34:45.000+08:00
- Modules that have no coverage at all are simply not included in the HTML
  reports generated by HPC.
- Add a warning to the project coverage report index page so users are aware of
  this limitation of HPC.
diff --git a/lib/cover-project.nix b/lib/cover-project.nix
@@ -24,6 +24,9 @@ let
       <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
     </head>
     <body>
+      <div>
+        WARNING: Modules with no coverage are not included in any of these reports, this is just how HPC works under the hood.
+      </div>
       <div>
         <h2>Union Report</h2>
         <p>The following report shows how each module is covered by any test in the project:</p>
