Improve Docker usage documentation

--rm removes the container right after running it, without the need to cleanup
-u $(id-u) runs as the current user, removing the need to modify permissions after

Author: ccremer

README.md

@@ -51,18 +51,15 @@ You can mount directory with charts under `/helm-docs` within container.
 Print generated documentation to stdout rather than modifying READMEs:
 
 ```bash
-docker run -v "$(pwd):/helm-docs" jnorwood/helm-docs:latest --dry-run
+docker run --rm -v "$(pwd):/helm-docs" -u $(id -u) jnorwood/helm-docs:latest --dry-run
 ```
 
 Overwrite READMEs within mounted directory:
 
 ```bash
-docker run -v "$(pwd):/helm-docs" jnorwood/helm-docs:latest
+docker run --rm -v "$(pwd):/helm-docs" -u $(id -u) jnorwood/helm-docs:latest
 ```
 
-Notice: You may need to fix permissions to the created files.
-
-
 # Building from source
 
 Notice that you need to have build chain toolkit for given platform and golang installed.