Fix Quadlet Options=key=value documentation/example

Quadlet `[Network]` does not accept `Options=key` for `podman network create --opt key`. Options have to be provided in `key=value` format, where the `=` is required even though the value may be empty.

One usage example is `Options=isolate=true`. In this case, passing `netavark` an empty `isolate` value may be a valid/parseable setting: `Options=isolate=`, equivalent to `Options=isolate=false`.

This commit documents the explicit `Options=key=value` usage. Compare to `[Network]` tests, which use `key=value`.

Usage verified locally by inspecting the generated network in `/run/user/${UID}/systemd/generator/example-network.service` and `podman network inspect systemd-example` using podman v4.9.2 and netavark v1.10.2.

See

- https://docs.podman.io/en/latest/markdown/podman-systemd.unit.5.html#network-units-network
- https://github.com/containers/podman/blob/v4.9.2/test/e2e/quadlet/options.network
- https://github.com/containers/podman/blob/v4.9.2/test/e2e/quadlet/options.multiple.network
- https://github.com/containers/netavark/blob/v1.10.2/src/network/bridge.rs#L824-L833

Signed-off-by: Joel Purra <mig@joelpurra.se>

docs/source/markdown/podman-systemd.unit.5.md

@@ -1070,7 +1070,7 @@ Valid options for `[Network]` are listed below:
 | IPv6=true                           | --ipv6                               |
 | Label="XYZ"                         | --label "XYZ"                        |
 | NetworkName=foo                     | podman network create foo            |
-| Options=isolate                     | --opt isolate                        |
+| Options=isolate=true                | --opt isolate=true                   |
 | PodmanArgs=--dns=192.168.55.1       | --dns=192.168.55.1                   |
 | Subnet=192.5.0.0/16                 | --subnet 192.5.0.0/16                |