Doc: update json_schema [ci skip]

doc/json_schema.json

@@ -23,7 +23,7 @@
             "default": 0
         },
         "format": {
-            "description": "Output format of the module. See `-h <module>-format` for detail",
+            "description": "Output format of the module. See `-h module-format` for detail",
             "type": "string"
         },
         "outputColor": {
@@ -89,10 +89,12 @@
             "default": "https://github.com/fastfetch-cli/fastfetch/raw/dev/doc/json_schema.json"
         },
         "logo": {
+            "description": "Fastfetch logo configurations\nSee also https://github.com/fastfetch-cli/fastfetch/wiki/Logo-options",
             "oneOf": [
                 {
                     "description": "Disable logo",
-                    "type": "null"
+                    "type": "null",
+                    "const": null
                 },
                 {
                     "description": "Set the source file of the logo",