[README.md] Improvement of background

[camillebloch]

In the Background section, i would suggest to improve de text to have a stronger link to the business.

First of all we are missing a clear definition of TSO and DSO, and we may also need to bring more context on specificities and challenges which need to be considered by SEAPATH, for example to explain what is a "Protection Automation and Control device" that there are strong realtime constraints (with exemples, because we are not talking about realtime as understood by IT).
We may also have to make relation to standards which will be in relation with SEAPATH, like IEC 61850 and IEC 62351.

[ebail]

@camillebloch I would suggest you to do a proposal.
I would suggest as an example to inform TSC of the proposal and ask them if they want to be involved in the approval or not