🎨 Improved GS001-DEPR-IMG rule description

refs #85

- reduce chance that people will misusage handlebars
  - {{if img_url feature_image}}

lib/spec.js

@@ -91,11 +91,12 @@ rules = {
     },
     "GS001-DEPR-IMG": {
         "level": "error",
-        "rule": "Replace the <code>{{image}}</code> helper with <code>{{img_url feature_image}}</code> or <code>{{img_url profile_image}}</code>",
+        "rule": "The <code>{{image}}</code> helper was replaced with the <code>{{img_url}}</code> helper. <b>Please read the details.</b></code>.",
         "fatal": true,
-        "details": "The <code>{{image}}</code> helper was replaced with <code>{{img_url}}</code>.<br>" +
+        "details": "The <code>{{image}}</code> helper was replaced with the <code>{{img_url}}</code> helper.<br>" +
                    "Depending on the context of the <code>{{img_url}}</code> helper you would need to use e. g. <br><br><code>{{#post}}<br>&nbsp;&nbsp;&nbsp;&nbsp;{{img_url feature_image}}<br>{{/post}}</code><br><br>to render the feature image of the blog post.<br>" +
-                   "Find more information about the <code>{{img_url}}</code> helper <a href=\"https://themes.ghost.org/docs/img_url\" target=_blank>here</a> and " +
+                   "<br><b>If you are using <code>{{if image}}</code></b>, then you have to replace it with e.g. <code>{{if feature_image}}.</code>" +
+                   "<br><br>Find more information about the <code>{{img_url}}</code> helper <a href=\"https://themes.ghost.org/docs/img_url\" target=_blank>here</a> and " +
                    "read more about Ghost's usage of contexts <a href=\"https://themes.ghost.org/docs/context-overview\" target=_blank>here</a>."
     },
     "GS001-DEPR-COV": {