Support for additional volumes and flags (#136)

* create/enter: support for additional volumes and flags
* docs: update docs and man pages to include new flags

docs/usage/distrobox-create.md

@@ -10,6 +10,8 @@ Usage:
 	distrobox-create --image registry.fedoraproject.org/fedora-toolbox:35 --name fedora-toolbox-35
 	distrobox-create --clone fedora-toolbox-35 --name fedora-toolbox-35-copy
 	distrobox-create --image alpine my-alpine-container
+	distrobox create --image fedora:35 --name test --volume /opt/my-dir:/usr/local/my-dir:rw --additional-flags "--pids-limit -1"
+	distrobox create --image fedora:35 --name test--additional-flags "--env MY_VAR-value"
 
 You can also use environment variables to specify container name and image
 
@@ -30,6 +32,32 @@ Options:
 				this will be useful to either rename an existing distrobox or have multiple copies
 				of the same environment.
 	--home/-H		select a custom HOME directory for the container. Useful to avoid host's home littering with temp files.
+	--volume		additional volumes to add to the container
+	--additional-flags/-a:	additional flags to pass to the container manager command
 	--help/-h:		show this message
 	--verbose/-v:		show more verbosity
 	--version/-V:		show version
+
+The `--additional-flags` or `-a` is useful to modify defaults in the container creations.
+For example:
+
+	distrobox create -i docker.io/library/archlinux -n dev-arch
+
+	podman container inspect dev-arch | jq '.[0].HostConfig.PidsLimit'
+	2048
+
+	distrobox rm -f dev-arch
+	distrobox create -i docker.io/library/archlinux -n dev-arch --volume $CBL_TC:/tc --additional-flags "--pids-limit -1"
+
+	podman container inspect dev-arch | jq '.[0].HostConfig,.PidsLimit'
+	0
+
+Additional volumes can be specified using the `--volume` flag. This flag follows the same standard as `docker` and `podman`
+to specify the mount point so `--volume SOURCE_PATH:DEST_PATH:MODE`.
+
+	distrobox create --image docker.io/library/archlinux --name dev-arch --volume /usr/share/:/var/test:ro
+
+During container creation, it is possible to specify (using the additional-flags) some environment variables that will
+persist in the container and be independent from your environment:
+
+	distrobox create --image fedora:35 --name test--additional-flags "--env MY_VAR-value"

docs/usage/distrobox-enter.md

@@ -10,6 +10,9 @@ Usage:
 
 	distrobox-enter --name fedora-toolbox-35 -- bash -l
 	distrobox-enter my-alpine-container -- sh -l
+	distrobox-enter --additional-flags "--preserve-fds" --name test -- bash -l
+	distrobox-enter --additional-flags "--env MY_VAR=value" --name test -- bash -l
+	MY_VAR=value distrobox-enter --additional-flags "--preserve-fds" --name test -- bash -l
 
 Supported environment variables:
 
@@ -20,8 +23,21 @@ Options:
 	--name/-n:		name for the distrobox						default: fedora-toolbox-35
 	--/-e:			end arguments execute the rest as command to execute at login	default: bash -l
 	--headless/-H:		do not instantiate a tty
+	--additional-flags/-a:	additional flags to pass to the container manager command
 	--help/-h:		show this message
 	--verbose/-v:		show more verbosity
 	--version/-V:		show version
 
 This is used to enter the distrobox itself. Personally, I just create multiple profiles in my `gnome-terminal` to have multiple distros accessible.
+
+
+The `--additional-flags` or `-a` is useful to modify default command when executing in the container.
+For example:
+
+	distrobox enter -n dev-arch --additional-flags "--env my_var=test" -- printenv &| grep my_var
+	my_var=test
+
+This is possible also using normal env variables:
+
+	my_var=test distrobox enter -n dev-arch --additional-flags -- printenv &| grep my_var
+	my_var=test