Updated Design: Dynamic node's icon (markdown)

Design:-Dynamic-node's-icon.md

@@ -84,14 +84,7 @@ Necessary actions to realize this proposal:
 ## Select icon
 User can select an icon on the node settings tab.  Once you click `OK` button, the node icon will change.
 
-## Unknown icon
-There are two cases that cause unknown icon.
-- Node-defined icon does not exist.
-  - Cause: The definition of a contribution node has a problem.
-  - Handling: Show arrow-in.png. (as is)
-- User-defined icon path does not exist although node-defined icon exists.
-  - Cause: Export a flow that uses an icon from a 3rd party module, and import the flow on the other Node-RED that does not install the 3rd party module.
-  - Handling: Show node-defined icon on behalf of user-defined icon. Show node-error.png icon on the top of the node, and surround the input field of icon in `node settings` section with red frame.
+Restriction: If a node has `icon` property by default, a user cannot select a user defined icon (e.g. ui_button node in node-red-dashboard).
 
 # API design
 ## Icon property of flow data
@@ -122,12 +115,14 @@ Returns a list of all icon files available in the editor for each module.
 }
 ```
 
+The icons in the following directory will be traversed when Node-RED starts running.
+- `icons` directory in the installed node module.
+- `$HOME/.node-red/lib/icons`
 
 # Candidates of enhancement
 - Add "enableIconChange" parameter in settings.js to enable/disable this feature.
   - Default value is true.
-- Enable it to choose font-awesome and material design icon.
-- Changeable node color
+- Enable it to choose font-awesome icon.
 - Show a node type:
   - during mouse over
   - in a small icon or string