fix: add layer to Dockerfile to fix issue 15394 (#15395)

get-started/09_image_best.md

@@ -107,6 +107,7 @@ Let's look at the Dockerfile we were using one more time...
 ```dockerfile
 # syntax=docker/dockerfile:1
 FROM node:12-alpine
+RUN apk add --no-cache python2 g++ make
 WORKDIR /app
 COPY . .
 RUN yarn install --production
@@ -127,6 +128,7 @@ a change to the `package.json`. Make sense?
     ```dockerfile
     # syntax=docker/dockerfile:1
     FROM node:12-alpine
+    RUN apk add --no-cache python2 g++ make
     WORKDIR /app
     COPY package.json yarn.lock ./
     RUN yarn install --production