docs: document Docker advanced setup

doc/docker.md

@@ -14,3 +14,80 @@ kcov needs access the following system calls:
 - [`personality`](https://linux.die.net/man/2/personality)
 
 You may need to use `--security-opt seccomp=unconfined` as a docker run option to attach to processes.
+
+## Copy into your image
+
+You may want to copy kcov into your image to avoid building it.
+
+```Dockerfile
+# Copy kcov (use kcov/kcov:latest-alpine for Alpine based images)
+COPY --from=kcov/kcov:latest /usr/local/bin/kcov* /usr/local/bin/
+# If you need documentation
+COPY --from=kcov/kcov:latest /usr/local/share/doc/kcov /usr/local/share/doc/kcov
+```
+
+### Python + bats example
+
+```Dockerfile
+# The base layer of your image
+FROM python:3.11-slim-bookworm
+
+# Install kcov run-time dependencies and bats.
+RUN apt-get update && \
+    apt-get install --yes --no-install-suggests --no-install-recommends \
+      libbfd-dev \
+      libcurl4 \
+      libdw1 \
+      zlib1g \
+      bats \
+      && \
+    apt-get clean && \
+    rm -rf /var/lib/apt/lists/*
+
+# Copy kcov (use kcov/kcov:latest-alpine for Alpine based images)
+COPY --from=kcov/kcov:latest /usr/local/bin/kcov* /usr/local/bin/
+COPY --from=kcov/kcov:latest /usr/local/share/doc/kcov /usr/local/share/doc/kcov
+
+WORKDIR /code
+
+CMD ["bats"]
+```
+
+#### Test it
+
+##### `test.sh`
+
+```sh
+#!/usr/bin/env bats
+
+source script.sh
+
+@test "test outputNumber function" {
+  result="$( outputNumber )"
+  [ "$result" -eq 7 ]
+}
+
+@test "kcov version" {
+  kcov --version | grep -q -c -F "v"
+  [ "$?" -eq 0 ]
+}
+```
+
+##### `script.sh`
+
+```sh
+outputNumber() {
+  echo 7
+}
+```
+
+##### Run tests
+
+```sh
+# build our image
+docker build ./ -t py-bats
+# test the built image
+docker run --rm -it -v $PWD:/code py-bats kcov --include-path=/code --dump-summary ./coverage bats ./test.sh
+# See the coverage result in ./coverage
+# Browse file:///tmp/kcov/coverage/index.html in your browser
+```