net_convert: add some missing help text

[OddBloke]

Proposed Commit Message

net_convert: add some missing help text

Test Steps

You can run this in a local checkout; here's the output diff:

--- before	2021-01-06 16:23:47.951011650 -0500
+++ after	2021-01-06 16:23:51.771062044 -0500
@@ -7,7 +7,9 @@
 optional arguments:
   -h, --help            show this help message and exit
   -p PATH, --network-data PATH
+                        The network configuration to read
   -k {eni,network_data.json,yaml,azure-imds,vmware-imc}, --kind {eni,network_data.json,yaml,azure-imds,vmware-imc}
+                        The format of the given network config
   -d PATH, --directory PATH
                         directory to place output in
   -D {alpine,arch,debian,ubuntu,freebsd,gentoo,amazon,centos,fedora,rhel,opensuse,sles}, --distro {alpine,arch,debian,ubuntu,freebsd,gentoo,amazon,centos,fedora,rhel,opensuse,sles}
@@ -15,3 +17,4 @@
                         interface name to mac mapping
   --debug               enable debug logging to stderr.
   -O {eni,netplan,sysconfig}, --output-kind {eni,netplan,sysconfig}
+                        The network config format to emit

Checklist:

• My code follows the process laid out in the documentation
• I have updated or added any unit tests accordingly
• I have updated or added any documentation accordingly