chore(doc): hot reload imported files (#417)

* [doc] Hot reload imported files

[doc] Hot reload imported files
Issue #267

* Update importer-guidelines.md

PR suggestions.

importer-guidelines.md

@@ -738,3 +738,16 @@ export default {
 ```
 
 Just add the extra styles you need to perform your transformation.
+
+### Hot reload of JS Dependencies
+
+It is common to use multiple files for the import process, usually using `import.js` as the entry.  By default, the UI will only hot reload changes in the "Transformation file URL" specified in the UI (i.e. import.js) and *not* its 'imports' which forces the user to refresh whenever dependencies are changed. To enable hot reload of dependencies, `esbuild` can be used with the watch option.
+
+- Ensure `esbuild` is installed and accessible.
+- From the command line, start `esbuild` as follows (varying paths and/or parameters as required):
+  - `esbuild import.js --bundle --outdir=importjs --watch`
+  - This will watch for changes on import.js **and** all its imports, bundling them in the specified `outdir`.
+- In the Importer UI, change the transformation file indicated to the one that is built in the output dir.
+
+Now the UI will load the bundled JS file, which will be automatically built when any changes are made.
+