List server requirements (=needed commands, e.g. rsync, readlink) in docs

[rintisch]

I wanted to use deployer and had multiple problem with using it because the tool uses multiple linux commands that are not given on every webspace hosting package.
I had to contact the support multiple times to ask them adding the commands that are used by deployer.

Up to now this were:

• rsync
• readlink

I don't know whether more might come but it would have been cool to have a central place to see which commands are used to test this beforehand.

[antonmedv]

Ohh readlink? It should be avialable by default.

[rintisch]

Unfortunately not everywhere :-/