docs: add example of 2john tools with Docker (#761)

It is possible to run some 2john tools directly from the Docker image.

The Docker image does not have Python or Lua installed, so it is not
possible to run scripts using this approach.

Signed-off-by: Claudio André <[email protected]>

Author: claudioandre-br

docs/examples-docker.md

@@ -57,6 +57,21 @@ Using the `--rm` flag to clean up the container and remove the file system after
  -rw------- 1 claudio users  246 jun 20 08:59 john.rec
 ```
 
+## Execute compiled 2john tools
+
+It is possible to run some 2john tools directly from the Docker image. Example:
+
+```bash
+# If necessary, update the local Docker image
+docker pull ghcr.io/openwall/john:bleeding
+
+# To extract the relevant information from (e.g.) a zip file
+docker run -v $(pwd):/host --rm -w /host --entrypoint /john/run/zip2john ghcr.io/openwall/john:bleeding /host/file.zip
+
+# Or
+docker run -v $(pwd):/host --rm -w /host --entrypoint /john/run/zip2john ghcr.io/openwall/john:bleeding /host/file.zip > zip.hash
+```
+
 ## Compare the performance of SIMD extensions
 
 ```bash