Installation Manual updated

The Installation Manual got a major update. Most of the content from the old website has been transferred and updated, and new content has been added based on experience with installations at IAS. Please note there are still a few sections to fill, that will be done in the coming days.

As you know the manuals are generated from a GitHub repository plato-cgse-doc, so if you read something the is incorrect, or if you notice missing content, please open an issue on the repo or create a pull request with the fixed or updated content. We will be grateful for your contributions.