Add per-category details

layers/light_pollution.js

@@ -25,4 +25,5 @@ let layers = [];
 export default {
     name: "Light Pollution",
     layers: layers,
+    details: "For legend and more information, see <a href='https://www.cleardarksky.com/'>cleardarksky.com</a>.",
 };

main.js

@@ -28,6 +28,7 @@ for (let category of layerCategories) {
   catDiv.innerHTML = `
     <details ${category.layers.filter(l => l.enabled).length > 0 ? "open" : ""}>
     <summary>${category.name}</summary>
+    ${category.details ? "<p>" + category.details + "</p>" : ""}
     <ul></ul>
     </details>
   `;