Update guide with minimum cli version info
Update guide with minimum cli version info

**What**
- Add a note indicating that `faas-cli>=0.5.1` is required for the
examples.

Signed-off-by: Lucas Roesler <beef10855a411edf7f10a2e0b798b93667a3aba8@gmail.com>

rgee0/faas,rgee0/faas,openfaas/faas,alexellis/faas,rgee0/faas,alexellis/faas,rgee0/faas,alexellis/faas,alexellis/faas,rgee0/faas,alexellis/faas,rgee0/faas,rgee0/faas,alexellis/faas,alexellis/faas,alexellis/faas,rgee0/faas,alexellis/faas,rgee0/faas,rgee0/faas,openfaas/faas,openfaas/faas