[requirements] Document code

src/modules/welcome/checker/RequirementsChecker.h

@@ -27,6 +27,15 @@
 class CheckerWidget;
 class QWidget;
 
+/**
+ * An indication of a requirement, which is checked in preparation
+ * for system installation. An entry has a name and some explanation,
+ * as well as three meaningful states:
+ *  - checked = true, the requirement is met (green)
+ *  - checked = false, the requirement is not met
+ *      - required = false, warn about it (yellow), no failure
+ *      - required = true, prohibit installation (red)
+ */
 struct PrepareEntry
 {
     QString name;