Merge branch 'sshdoc' into 'master'

Include non-default ssh key location info

Fixes #875

Provide help for people who aren't SSH-clued by indicating
how to point to key files that have been named something
other than the default. A lot of people seem to assume that
the filename they choose is irrelevant and then wonder why
their private key is not being found by simple 'ssh' commands.

See merge request !507