Adding new Vireo instruction documentation

[rajsite]

We have some tribal knowledge around adding new Vireo instructions that we should document. This issue will gather opinion / hold some of those until documentation is made:

1. All new instructions should use VIREO_FUNCTION_SIGNATURET or VIREO_FUNCTION_SIGNATUREV. These versions give you the ability to name parameters which makes Vireo instructions significantly more readable.

   Particularly we should be migrating away from usage of VIREO_FUNCTION_SIGNATURE0 through VIREO_FUNCTION_SIGNATURE10. (are there any reasons to prefer usage of the 0-10 signatures? @spathiwa @sanmut @cglzaguilar )