doc: add comment about transform in main index file

Author: etpinard

lib/index.js

@@ -32,6 +32,15 @@ Plotly.register([
 ]);
 
 // transforms
+//
+// Please note that all *transform* methods are executed before
+// all *calcTransform* methods - which could possibly lead to
+// unexpected results when applying multiple transforms of different types
+// to a given trace.
+//
+// For more info, see:
+// https://github.com/plotly/plotly.js/pull/978#pullrequestreview-2403353
+//
 Plotly.register([
     require('./filter'),
     require('./groupby')

src/plot_api/register.js

@@ -69,8 +69,6 @@ function registerTransformModule(newModule) {
         throw new Error(prefix + ' is missing a *transform* or *calcTransform* method.');
     }
 
-    // For more info, see:
-    // https://github.com/plotly/plotly.js/pull/978#pullrequestreview-2403353
     if(hasTransform && hasCalcTransform) {
         Lib.log([
             prefix + ' has both a *transform* and *calcTransform* methods.',