Outdated documentation and the help

[kostas-kou]

Describe the bug
The repo's documentation is outdated and there are some errors, go through the documentation and make changes.
The help command should follow the docker style of help and add a link of the documentation for the specific version in the help command.

Steps to reproduce

Additional context
There is also an error in the description of the list sub command

./sda-cli -config <configuration_file> list --datasets --url <login_url> (--bytes)

login_url is wrong, should be download_url

Another one is in the download section:

./sda-cli -config download <configuration_file> -dataset-id <datasetID> -url <download-service-url> -outdir <outdir> <path/to/file1> <other/path/to/file2> ... (or <fileID_1> <fileID_2> ...)

the download should be after the <configuration_file>

Estimation of size: small

Estimation of priority: high