Make dev container compatible with podman

Following the issue described in InfiniTimeOrg#174 (comment).
This prevents permission issues when using the dev container with podman, which is running rootless. Usage with docker requires explicitly passing UID and GID of the local user, which is added to the README.

Author: dariusarnold

.devcontainer/Dockerfile

@@ -48,8 +48,6 @@ RUN SNIPPET="export PROMPT_COMMAND='history -a' && export HISTFILE=/commandhisto
     && chown -R $USERNAME /commandhistory \
     && echo "$SNIPPET" >> "/home/$USERNAME/.bashrc"
 
-USER ubuntu
-
 # Section for interactive compilation during docker run
 
 WORKDIR /sources

README.md

@@ -121,18 +121,18 @@ docker build -t infinisim-build .devcontainer
 
 Afterwards you can build the simulator with:
 ```sh
-docker run --rm -it -v ${PWD}:/sources infinisim-build
+docker run --rm -it -v ${PWD}:/sources --user $(id -u):$(id -g) infinisim-build
 ```
 
 By default this builds the simulator using the InfiniTime files from the submodule in your `${PWD}`.
 If you want to use a different repository, you got to mount it and pass the path to the `INFINITIME_DIR` variable:
 ```sh
-docker run --rm -it -v ${PWD}:/sources -v ${PWD}/../InfiniTime:/infinitime -e INFINITIME_DIR=/infinitime infinisim-build
+docker run --rm -it -v ${PWD}:/sources -v ${PWD}/../InfiniTime:/infinitime -e INFINITIME_DIR=/infinitime  --user $(id -u):$(id -g) infinisim-build
 ```
 
 Other CMake generation and build arguments can be passed to the `GENERATE_ARGS` and `BUILD_ARGS` variables:
 ```sh
-docker run --rm -it -v ${PWD}:/sources -e GENERATE_ARGS=-DENABLE_USERAPPS="Apps::Timer,Apps::Alarm" -e BUILD_ARGS=-j16 infinisim-build
+docker run --rm -it -v ${PWD}:/sources -e GENERATE_ARGS=-DENABLE_USERAPPS="Apps::Timer,Apps::Alarm" -e BUILD_ARGS=-j16 --user $(id -u):$(id -g)  infinisim-build
 ```