fix(cordova): warn about missing cordova-res when adding platforms

If cordova-res isn't installed, print a warning message about how to
install and what to do next.

ref: #4026

Author: imhoffd

packages/ionic/src/commands/cordova/platform.ts

@@ -3,7 +3,7 @@ import * as lodash from 'lodash';
 
 import { CommandInstanceInfo, CommandLineInputs, CommandLineOptions, CommandMetadata, CommandPreRun } from '../../definitions';
 import { input } from '../../lib/color';
-import { SUPPORTED_PLATFORMS } from '../../lib/cordova-res';
+import { SUPPORTED_PLATFORMS, createCordovaResNotFoundMessage, findCordovaRes } from '../../lib/cordova-res';
 import { FatalException } from '../../lib/errors';
 import { runCommand } from '../../lib/executor';
 
@@ -104,7 +104,18 @@ Like running ${input('cordova platform')} directly, but adds default Ionic icons
 
     if (action === 'add' && options['resources'] && SUPPORTED_PLATFORMS.includes(platformName)) {
       const args = ['cordova', 'resources', platformName, '--force'];
-      await runCommand(runinfo, args);
+      const p = await findCordovaRes();
+
+      if (p) {
+        await runCommand(runinfo, args);
+      } else {
+        this.env.log.warn(await createCordovaResNotFoundMessage(this.env.config.get('npmClient')));
+        this.env.log.warn(
+          `Cannot generate resources without ${input('cordova-res')} installed.\n` +
+          `Once installed, you can generate resources with the following command:\n\n` +
+          input(['ionic', ...args].join(' '))
+        );
+      }
     }
   }
 }