docs: Update instructions for python 3

Author: nschonni

docs/BestPractices.md

@@ -185,7 +185,7 @@ Here is an example of how you would install dependencies for packages that requi
 ```Dockerfile
 FROM node:alpine
 
-RUN apk add --no-cache --virtual .gyp python make g++ \
+RUN apk add --no-cache --virtual .gyp python3 make g++ \
     && npm install [ your npm dependencies here ] \
     && apk del .gyp
 ```
@@ -196,7 +196,7 @@ And Here's a multistage build example
 FROM node:alpine as builder
 
 ## Install build toolchain, install node deps and compile native add-ons
-RUN apk add --no-cache python make g++
+RUN apk add --no-cache python3 make g++
 RUN npm install [ your npm dependencies here ]
 
 FROM node:alpine as app