Update Alpine instructions (coder#7156)

While trying to set up code-server on Alpine, I ran into build errors. To solve them, I had to add Kerberos development libs. Also, it looks like npm config doesn't work in recent version of Node and doesn't seem to be necessary. These instructions were tested in the Docker `node:20-alpine` image.

Author: jpetazzo

docs/npm.md

@@ -62,8 +62,7 @@ Proceed to [installing](#installing)
 ## Alpine
 
 ```bash
-apk add alpine-sdk bash libstdc++ libc6-compat
-npm config set python python3
+apk add alpine-sdk bash libstdc++ libc6-compat python3 krb5-dev
 ```
 
 Proceed to [installing](#installing)