README: Provide more execution examples

[nodeg]

Description

It would be nice to have more examples in the README, e.g. for building the current docs for Uyuni.

Example

For SUMA I run

./uyuni-docs-helper -o suma -c obs-packages-suma-en -p suma

but I do not clearly see what command (-c) I need to use for Uyuni.

The help is not clear on that:

❯ ./uyuni-docs-helper -h

Build the Uyuni doc using a container and (optionally) serve it for verification via HTTP

Syntax:

uyuni-docs-helper <ARGUMENTS>

Mandatory arguments:

-p|--product <uyuni|suma>   Build the documentation for either Uyuni or SUSE Manager
-c|--command <make command> Use the desired command to build html/pdf, html&pdf, etc...
                            for example: 'all-uyuni'. You can use 'help' to list all
                            possible commands. Be aware you still need to specify
                            one source for this to work
(...)

Maybe we could also add all the possible commands to the help menu, too.