doc: document the added --build-tag option for the create subcommand

Author: KilianHanich

doc/toolbox-create.1.md

@@ -9,6 +9,7 @@ toolbox\-create - Create a new Toolbx container
                [*--image NAME* | *-i NAME*]
                [*--release RELEASE* | *-r RELEASE*]
                [*--build BUILDCONTEXT* | *-b BUILDCONTEXT*]
+               [*--build-tag TAG* | *-t TAG*]
                [*CONTAINER*]
 
 ## DESCRIPTION
@@ -119,6 +120,14 @@ by extracting the name from the image and then creates the container like normal
 
 You cannot use `--distro`, `--release` or `--image` together with this option.
 
+**--build-tag** TAG, **-t** TAG
+
+Overwrites the tagging behaviour of `--build` by tagging the image with TAG via
+`podman build --tag`. If no repository if given or podman doesn't know it,
+localhost is used.
+
+Can only be used when `--build` is also used.
+
 ## EXAMPLES
 
 ### Create the default Toolbx container matching the host OS