Metadirectives kernels fixup

[sbryngelson]

Following #926 -- the substitute of GPU_PARALLEL() for !$acc kernels does not work. A fix is needed. I do notice that the current fypp macro creates this kind of code

!$acc parallel default(present)
<code>
!$acc end parallel

I wonder if default(present) is the issue here. I think !$acc parallel alone might be OK, but have not tested it. Either way, it seems like having kernels be an option is somehow useful.

[wilfonba]

The documentation for this is also missing from the website. I believe the docs/documentation/readme.md needs the line - [GPU Parallelization](gpuParallelization.md) added to the table of contents for it to show up.

[sbryngelson]

yes indeed good catch @wilfonba

[wilfonba]

This file (https://github.com/MFlowCode/MFC/blob/master/.cursor/rules/mfc-agent-rules.mdc) also needs updated.