add in a Dockerfile to build linux binaries

Based on
https://gist.github.com/rlefevre/1523f47e75310e28eee243c9c5651ac9 by
@rlefevre. Thank you so much!

Author: evancz

installers/linux/Dockerfile

@@ -0,0 +1,22 @@
+FROM alpine:3.10
+
+# branch
+ARG branch=master
+# commit or tag
+ARG commit=HEAD
+
+# Install required packages
+RUN apk add --update ghc cabal git musl-dev zlib-dev ncurses-dev ncurses-static wget
+
+# Checkout elm compiler
+WORKDIR /tmp
+RUN git clone -b $branch https://github.com/elm/compiler.git
+
+# Build a statically linked elm binary
+WORKDIR /tmp/compiler
+RUN git checkout $commit
+RUN rm worker/elm.cabal
+RUN cabal new-update
+RUN cabal new-configure --disable-executable-dynamic --ghc-option=-optl=-static --ghc-option=-optl=-pthread
+RUN cabal new-build
+RUN strip -s ./dist-newstyle/build/x86_64-linux/ghc-8.4.3/elm-0.19.1/x/elm/build/elm/elm