added devcontainer files

.devcontainer/Dockerfile

@@ -0,0 +1,43 @@
+FROM ubuntu:18.04
+
+ARG DEBIAN_FRONTEND=noninteractive
+RUN apt-get update -qq \
+    && apt-get install -y \
+# x86_64 / generic packages
+      bash \
+      build-essential \
+      cmake \
+      git \
+      make \
+      python3 \
+      python3-pip \
+      tar \
+      unzip \
+      wget \ 
+      curl \
+# aarch64 packages
+      libffi-dev \
+      libssl-dev \
+      python3-dev \ 
+      rustc \
+    && rm -rf /var/cache/apt/* /var/lib/apt/lists/*;
+
+RUN adduser infinitime
+
+RUN pip3 install adafruit-nrfutil
+# required for McuBoot
+RUN pip3 install setuptools_rust
+
+WORKDIR /opt/
+# build.sh knows how to compile
+COPY build.sh .
+
+# Lets get each in a separate docker layer for better downloads
+# GCC
+RUN bash -c "source /opt/build.sh; GetGcc;"
+# NrfSdk
+RUN bash -c "source /opt/build.sh; GetNrfSdk;"
+# McuBoot
+RUN bash -c "source /opt/build.sh; GetMcuBoot;"
+
+ENV SOURCES_DIR /workspaces/Pinetime