Added Note on Docker Usage

No mention was yet made regarding the installation errors that may occur if a user attempts to install opencv4nodejs onto the Docker image, so I propose adding a small change to notify users of the likelihood of said errors and two workarounds.

Author: lummish

README.md

@@ -141,6 +141,8 @@ Or simply pull from [justadudewhohacks/opencv-nodejs](https://hub.docker.com/r/j
 FROM justadudewhohacks/opencv-nodejs
 ```
 
+**Note**: The aforementioned Docker image does not have build tools installed. In order to prevent errors during an ```npm install```, you can either install opencv4nodejs globally and link to it in your project or install production packages only in your Dockerfile.
+
 Different OpenCV 3.x base images can be found here: https://hub.docker.com/r/justadudewhohacks/.
 
 <a name="usage-with-electron"></a>
@@ -502,4 +504,4 @@ const cv = require('opencv4nodejs')
 * <a href="https://justadudewhohacks.github.io/opencv4nodejs/docs/SIFTDetector#SIFTDetector"><b>xfeatures2d</b></a>
 * <a href="https://justadudewhohacks.github.io/opencv4nodejs/docs/MultiTracker#MultiTracker"><b>tracking</b></a>
 * <a href="https://justadudewhohacks.github.io/opencv4nodejs/docs/OCRHMMClassifier#OCRHMMClassifier"><b>text</b></a>
-* <a href="https://justadudewhohacks.github.io/opencv4nodejs/docs/EigenFaceRecognizer#EigenFaceRecognizer"><b>face</b></a>
+* <a href="https://justadudewhohacks.github.io/opencv4nodejs/docs/EigenFaceRecognizer#EigenFaceRecognizer"><b>face</b></a>