Merge pull request #3463 from ndeloof/cp_docs

improve cp documentation with some illustration examples

docs/reference/commandline/cp.md

@@ -89,6 +89,28 @@ you must be explicit with a relative or absolute path, for example:
 
     `/path/to/file:name.txt` or `./file:name.txt`
 
+## Examples
+
+Copy a local file into container
+
+```console
+$ docker cp ./some_file CONTAINER:/work 
+```
+
+Copy files from container to local path
+
+```console
+$ docker cp CONTAINER:/var/logs/ /tmp/app_logs
+```
+
+Copy a file from container to stdout. Please note `cp` command produces a tar stream
+
+```console
+$ docker cp CONTAINER:/var/logs/app.log - | tar x -O | grep "ERROR"
+```
+
+### Corner cases
+
 It is not possible to copy certain system files such as resources under
 `/proc`, `/sys`, `/dev`, [tmpfs](run.md#mount-tmpfs---tmpfs), and mounts created by
 the user in the container. However, you can still copy such files by manually