[odb-users] Out of sync documentation

[Danya Patrushev]

There seems to be a discrepancy between the manuals regarding the --
generate-schema-only option.
The odb compiler doc says:

--generate-schema-only
Generate only the database schema. Note that this option is only valid
when generating schema as a standalone SQL file (see --schema-format
for details).
While the odb manual contains  lines in chapter 13.1 Object Model
Version and Changelog:
The same can be achieved for the embedded schema by instructing the ODB
compiler to generate the database creation code into a separate C++
file (--schema-format separate):
odb --database pgsql --generate-schema-only --schema-format separate \
--at-once --input-name company person.hxx employee.hxx employer.hxx