Improve title of the standard document (add "FMI" ...)

[GallLeo]

The current heading of the document states

Layered Standard for XCP
(https://github.com/modelica/fmi-ls-xcp/blob/main/docs/index.adoc#layered-standard-for-xcp)

The readme states

FMI Layered Standard XCP (fmi-ls-xcp)
(https://github.com/modelica/fmi-ls-xcp)

From my point of view, the heading should

• include "FMI",
• maybe include the abbreviation "fmi-ls-xcp" (at least the abbreviation should be written somewhere in the document)
• Gramatically work for all currently planned layered standards. Current status:
  • fmi-ls-bus:
    • adoc: "Layered Standard for Network Communication"
    • readme: "FMI Layered Standard Network Communication"
  • fmi-ls-ref
    • adoc: "FMI Layered Standard REF"
    • readme: "Layered Standard References"
  • fmi-ls-struct
    • adoc: "fmi-ls-struct"
    • readme: "Layered Standard for Structured Data"

Taking all this into consideration, my proposal for the title would be:
"FMI Layered Standard for XCP (fmi-ls-xcp)"