[Documentation] Add a syntax description of USE commands for VFP dialects.

[vfp9]

While the syntax of the USE command is available in the existing documentation, it appears that, based on the version history description in the documentation (Ver 2.20.03: Fixed problem with the USE command with an AGAIN clause in the FoxPro dialect (#235)), it seems that for the VFP dialect, it appears that There is syntax that is inconsistent with the existing documentation.

[RobertvanderHulst]

I think we need separate help topics for the USE command in VFP syntax and the VO syntax.