Document how entrypoint is configured in buildah config

Fixes: #5598

Signed-off-by: Daniel J Walsh <[email protected]>

docs/buildah-config.1.md

@@ -77,6 +77,28 @@ ignore the `cmd` value of the container image.  However if you use the array
 form, then the cmd will be appended onto the end of the entrypoint cmd and be
 executed together.
 
+Note: The string form will be added executed via `sh -c`, where the array form
+will not use the containers shell.
+
+String Format:
+```
+$ buildah from scratch
+$ buildah config --entrypoint "/usr/bin/notashell" working-container
+$ buildah inspect --format '{{ .OCIv1.Config.Entrypoint }}' working-container
+[/bin/sh -c /usr/bin/notshell]
+$ buildah inspect --format '{{ .Docker.Config.Entrypoint }}' working-container
+[/bin/sh -c /usr/bin/notshell]
+```
+
+Array Format:
+```
+$ buildah config --entrypoint '["/usr/bin/notashell"]' working-container
+$ buildah inspect --format '{{ .OCIv1.Config.Entrypoint }}' working-container
+[/usr/bin/notashell]
+$ buildah inspect --format '{{ .Docker.Config.Entrypoint }}' working-container
+[/usr/bin/notashell]
+```
+
 **--env**, **-e** *env[=value]*
 
 Add a value (e.g. env=*value*) to the environment for containers based on any