Add use of template to Install command

[Waterdrips]

The tamplate name wasnt used, so
the command gave an error saying that
no template was used.

Signed-off-by: Alistair Hey alistair@heyal.co.uk

Tested:
BEFORE:

root@raspberrypi:~/go/src/github.com/alexellis/faasd# sudo faasd install
Error: error loading template ./hack/faas-containerd.service, error template: no files named in call to ParseFiles

AFTER:

root@raspberrypi:~/go/src/github.com/alexellis/faasd# sudo ./faasd install
root@raspberrypi:~/go/src/github.com/alexellis/faasd# 

[alexellis]

Thanks for this PR 👍

The tamplate name wasnt used, so
the command gave an error saying that
no template was used.

Could you fix the typo and wrap to 80 chars for the error messages? I use the text under the commit message as a guide on length.

i.e.

# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.

[alexellis]

Thanks for reformatting the commit message again, it is 72 chars not 80 (I was wrong)