add Dockerfile

docker/README.md

+# Docker
+
+Docker image for gcli is useful for people with docker-based infrastructure or old system with old glibc or libssl.
+
+## Build
+
+```sh
+./docker/build.sh
+```
+
+## Use
+
+To use gcli, run it with docker:
+
+```sh
+docker run --rm gcli
+```
+
+Ğcli uses folders to store config and vault. You can bind local folders to these locations:
+
+```sh
+# create folders
+mkdir -p $HOME/.config/gcli/
+mkdir -p $HOME/.local/share/gcli/
+# run gcli in docker with there folders
+docker run --rm \
+--mount type=bind,src=$HOME/.config/gcli/,dst=/root/.config/gcli \
+--mount type=bind,src=$HOME/.local/share/gcli/,dst=/root/.local/share/gcli \
+gcli
+```
+
+An alias can be useful:
+
+```sh
+# define alias
+alias docker_gcli="docker run --rm \
+--mount type=bind,src=$HOME/.config/gcli/,dst=/root/.config/gcli \
+--mount type=bind,src=$HOME/.local/share/gcli/,dst=/root/.local/share/gcli \
+gcli"
+# then simply call
+docker_gcli --help
+```