better 2-staged Dockerfile for development

Dockerfile

@@ -6,12 +6,12 @@ RUN mkdir -p $WORKDIR
 
 WORKDIR $WORKDIR
 
-ADD . .
-
 RUN apt-get update
 
-RUN apt-get install -y bc build-essential dkms
+RUN apt-get install -y bc build-essential dkms linux-headers-$(uname -r)
 
-CMD /bin/bash
+FROM build
+
+ADD . .
 
-# make KVER=4.15.0-46-generic
+CMD /bin/bash