Update docs/custom-templates.md

Co-authored-by: Sine Jespersen <[email protected]>

Author: tuj

docs/custom-templates.md

@@ -19,7 +19,7 @@ How you populate this folder with your custom templates is up to you:
 The following files are required for a custom template:
 
 * `custom-template-name.jsx` - A javascript module for the template.
-* custom-template-name.json - A configuration file for the template.
+* `custom-template-name.json` - A configuration file for the template.
 
 Replace `custom-template-name` with a unique name for the template.