Hint enabling cache if not already enabled.

src/index.js

@@ -1,9 +1,10 @@
-import { Action, Docker, Input, ImageTag, BuildParameters } from './model';
+import { Action, BuildParameters, Cache, Docker, Input, ImageTag } from './model';
 
 const core = require('@actions/core');
 
 async function action() {
   Action.checkCompatibility();
+  Cache.verify();
 
   const { dockerfile, workspace, builderFolder } = Action;
   const buildParameters = BuildParameters.create(Input.getFromUser());

src/model/cache.js

@@ -0,0 +1,23 @@
+import fs from 'fs';
+import Action from './action';
+import Project from './project';
+
+class Cache {
+  static verify() {
+    if (!fs.existsSync(Project.libraryFolder)) {
+      this.notifyAboutCachingPossibility();
+    }
+  }
+
+  static notifyAboutCachingPossibility() {
+    if (Action.isRunningLocally) {
+      return;
+    }
+
+    console.log('Library folder does not exist.');
+    console.log('Consider setting up caching to speed up your workflow.');
+    console.log('If this is not your first build.');
+  }
+}
+
+export default Cache;

src/model/cache.test.js

@@ -0,0 +1,9 @@
+import Cache from './cache';
+
+describe('Cache', () => {
+  describe('Verification', () => {
+    it('does not throw', () => {
+      expect(() => Cache.verify()).not.toThrow();
+    });
+  });
+});

src/model/index.js

@@ -1,8 +1,9 @@
 import Action from './action';
 import BuildParameters from './build-parameters';
+import Cache from './cache';
 import Docker from './docker';
 import Input from './input';
 import ImageTag from './image-tag';
 import Platform from './platform';
 
-export { Action, BuildParameters, Docker, Input, ImageTag, Platform };
+export { Action, BuildParameters, Cache, Docker, Input, ImageTag, Platform };