Update Kontact web site with info related to the Blue Angel criteria
The Blue Angel criteria ask for documentation of installation, uninstallation, modularity, transparency and privacy. This merge request adds a bit of information to the Kontact web site to make this more discoverable and clear.
The merge request also fixes a few small issues with the web sites, so that it renders correctly.
This relates to the KMail application for the Blue Angel, specifically the documentation requirements (https://invent.kde.org/cschumac/blue-angel-application/-/issues/55), which are part of the criteria for the Blue Angel for Resource and Energy-Efficient Software Products.