Add example for a catalog section

homepage_config.json.example

 {
   "sections": [
     {
-      "name": "my-catalog",
-      "title": "My catalog of schemas",
+      "name": "schema-catalog",
+      "title": "A catalog of schemas",
+      "description": "This is a catalog of schemas that is published somewhere. (Note: the catalog must be conform to this schema: https://opendataschema.frama.io/catalog/schema-catalog.json",
+      "catalog": "https://git.opendatafrance.net/scdl/catalog/raw/master/catalog.json"
+    },
+    {
+      "name": "schema-list",
+      "title": "A list of schemas",
+      "description": "This is a list of other schemas.",
       "catalog": {
         "version": 1,
         "schemas": [
@@ -28,8 +35,8 @@
     },
     {
       "name": "external",
-      "title": "External schemas",
-      "description": "A selection of validation tools",
+      "title": "A list of links to external validators",
+      "description": "This is a selection of validation tools that complement Validata.",
       "links": [
         {
           "name": "inspire",
@@ -48,4 +55,4 @@
       ]
     }
   ]
-}
\ No newline at end of file
+}