Update README

[haerdib]

Updates the README. Removed manual steps, but provided some necessary info (where to find id & cmds) to start it manually, in case it's necessary.

closes #92

[echevrier]

Thank you very much. It is much better. The commands are valid and working. But I am missing some info, in case something goes wrong.
The references to the substrate documentation are good, but it is unpleasant that in order to ensure that the different steps work as they should, you always have to refer to them.

[haerdib]

I'm not explaining the things too in depth, because I don't think this is a tutorial for beginners. There are tutorials from substrate to cover the basics, such as the meaning of the different ports and similar. This is a README for developers that know how starting a parachain works, but don't necessarily know all commands by heart yet.

So as long as the commands in the README work, that is good enough. Covering all necessary debugging information would require a lot more work. Which might get outdated quite soon again.

[echevrier]

Thanks.

[brenzi]

I would prefer if we set a team standard here. Go with the second option but explain how to install it that way

[haerdib]

Updated it accordingly. The installation needs to be globally such that the 2nd option can be used. But that's already in the installation part of polkadot-launch. So I simply put a Link there. Is that alright?

[brenzi]

whereas "global" means "across all projects of the current user", not system-wide for all users. then it's ok as it does not demand special privileges
~/.yarn/bin/polkadot-launch

[haerdib]

Yes, it's per user. At least if yarn has been installed for per-user. It didn't require any sudo command, in my case, neither for yarn nor for polkadot-launch with -g option.

[brenzi]

I like the simplification and decluttering.