Item search POST clarification

[cholmes]

Related Issue(s): #

Proposed Changes:

1. Added language to make it clearer how to indicate POST can be used.

PR Checklist:

• This PR is made against the dev branch (all proposed changes except releases should be against dev, not master).
• This PR has no breaking changes.
• I have added my changes to the CHANGELOG or a CHANGELOG entry is not required.
• OpenAPI files only: I have run npm run generate-all to update the generated OpenAPI files.

[cholmes]

@m-mohr - I hadn't realized you put the method thing in until after I submitted #77 I like the approach (hadn't really understood it). But I wasn't sure if you were supposed to add two links or one. My guess is two, so did that here, and tried for a little more clarity on required vs not. If I have it wrong let me know and I can try again.

[m-mohr]

With the one requested change good to be merged.