add npm install bluebird package in image display tutorial

content/en/tutorial/7688_imagedisplay_tutorial.md

@@ -88,11 +88,18 @@ opkg update
 opkg install fswebcam
 ```
 
-4. Try to capture a screenshot.
+4. Install the `mcsjs` and `bluebird` package.
+```
+npm install mcsjs
+npm install bluebird --save
+```
+
+5. Try to capture a screenshot.
 ```
 fswebcam -i 0 -d v4l2:/dev/video0 --no-banner -p YUYV --jpeg 95 --save /tmp/test.jpg
 ```
 
+
 Then you will see a test.jpg file in your root directory.
 
 **Hint:** Some of you may wonder why we need to store the file to /tmp/test.jpe. The reason is bebause the limitation of the flash on the LinkIt Smart 7688 development board. If we frequently write data to the flash, it will reduce the lifetime of the flash. That is why we suggest to store in the memory where /tmp folder is under. Also, please be reminded that the flash will be reset once no power supplied.

content/zh-CN/tutorial/7688_imagedisplay_tutorial.md

@@ -88,7 +88,13 @@ opkg update
 opkg install fswebcam
 ```
 
-4. Try to capture a screenshot.
+4. Install the `mcsjs` and `bluebird` package.
+```
+npm install mcsjs
+npm install bluebird --save
+```
+
+5. Try to capture a screenshot.
 ```
 fswebcam -i 0 -d v4l2:/dev/video0 --no-banner -p YUYV --jpeg 95 --save /tmp/test.jpg
 ```

content/zh-TW/tutorial/7688_imagedisplay_tutorial.md

@@ -88,7 +88,13 @@ opkg update
 opkg install fswebcam
 ```
 
-4. Try to capture a screenshot.
+4. Install the `mcsjs` and `bluebird` package.
+```
+npm install mcsjs
+npm install bluebird --save
+```
+
+5. Try to capture a screenshot.
 ```
 fswebcam -i 0 -d v4l2:/dev/video0 --no-banner -p YUYV --jpeg 95 --save /tmp/test.jpg
 ```