The parameter value for '--accept' is no UNO-Url, but uses a
similar syntax. This was wrongly changed in commit d78f29ab
("tdf#100836 "Starting the LibreOffice Software With Parameters"
help update").

So this changes the parameter value back to {accept-string},
documents its syntax and adds some common examples.

Change-Id: If8159b1d982c54e3dca6d27a1c400d2450ff2d1e
Reviewed-on: https://gerrit.libreoffice.org/72859Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Tested-by: Jenkins