docs: podman-build --network add slirp and pasta

Support was added in buildah some weeks ago. [1]

[1] https://github.com/containers/buildah/pull/4877

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

docs/source/markdown/podman-build.1.md.in

@@ -438,6 +438,52 @@ considered insecure.
 - **ns:**_path_: path to a network namespace to join.
 - **private**: create a new namespace for the container (default)
 - **\<network name|ID\>**: Join the network with the given name or ID, e.g. use `--network mynet` to join the network with the name mynet. Only supported for rootful users.
+- **slirp4netns[:OPTIONS,...]**: use **slirp4netns**(1) to create a user network stack. This is the default for rootless containers. It is possible to specify these additional options, they can also be set with `network_cmd_options` in containers.conf:
+  - **allow_host_loopback=true|false**: Allow slirp4netns to reach the host loopback IP (default is 10.0.2.2 or the second IP from slirp4netns cidr subnet when changed, see the cidr option below). The default is false.
+  - **mtu=MTU**: Specify the MTU to use for this network. (Default is `65520`).
+  - **cidr=CIDR**: Specify ip range to use for this network. (Default is `10.0.2.0/24`).
+  - **enable_ipv6=true|false**: Enable IPv6. Default is true. (Required for `outbound_addr6`).
+  - **outbound_addr=INTERFACE**: Specify the outbound interface slirp binds to (ipv4 traffic only).
+  - **outbound_addr=IPv4**: Specify the outbound ipv4 address slirp binds to.
+  - **outbound_addr6=INTERFACE**: Specify the outbound interface slirp binds to (ipv6 traffic only).
+  - **outbound_addr6=IPv6**: Specify the outbound ipv6 address slirp binds to.
+- **pasta[:OPTIONS,...]**: use **pasta**(1) to create a user-mode networking
+    stack. \
+    This is only supported in rootless mode. \
+    By default, IPv4 and IPv6 addresses and routes, as well as the pod interface
+    name, are copied from the host. If port forwarding isn't configured, ports
+    are forwarded dynamically as services are bound on either side (init
+    namespace or container namespace). Port forwarding preserves the original
+    source IP address. Options described in pasta(1) can be specified as
+    comma-separated arguments. \
+    In terms of pasta(1) options, **--config-net** is given by default, in
+    order to configure networking when the container is started, and
+    **--no-map-gw** is also assumed by default, to avoid direct access from
+    container to host using the gateway address. The latter can be overridden
+    by passing **--map-gw** in the pasta-specific options (despite not being an
+    actual pasta(1) option). \
+    Also, **-t none** and **-u none** are passed to disable
+    automatic port forwarding based on bound ports. Similarly, **-T none** and
+    **-U none** are given to disable the same functionality from container to
+    host. \
+    Some examples:
+    - **pasta:--map-gw**: Allow the container to directly reach the host using the
+        gateway address.
+    - **pasta:--mtu,1500**: Specify a 1500 bytes MTU for the _tap_ interface in
+        the container.
+    - **pasta:--ipv4-only,-a,10.0.2.0,-n,24,-g,10.0.2.2,--dns-forward,10.0.2.3,-m,1500,--no-ndp,--no-dhcpv6,--no-dhcp**,
+        equivalent to default slirp4netns(1) options: disable IPv6, assign
+        `10.0.2.0/24` to the `tap0` interface in the container, with gateway
+        `10.0.2.3`, enable DNS forwarder reachable at `10.0.2.3`, set MTU to 1500
+        bytes, disable NDP, DHCPv6 and DHCP support.
+    - **pasta:-I,tap0,--ipv4-only,-a,10.0.2.0,-n,24,-g,10.0.2.2,--dns-forward,10.0.2.3,--no-ndp,--no-dhcpv6,--no-dhcp**,
+        equivalent to default slirp4netns(1) options with Podman overrides: same as
+        above, but leave the MTU to 65520 bytes
+    - **pasta:-t,auto,-u,auto,-T,auto,-U,auto**: enable automatic port forwarding
+        based on observed bound ports from both host and container sides
+    - **pasta:-T,5201**: enable forwarding of TCP port 5201 from container to
+        host, using the loopback interface instead of the tap interface for improved
+        performance
 
 #### **--no-cache**