Update ScatterPlotViewer README

[lcjohnso]

Describe your changes

Updates out-of-date documentation for the ScatterPlotViewer to clarify that all coordinate data should be passed using seriesData structure, not just in the case of wanting to support multiple series. The updates also clarify differences between the PH TESS LightCurveViewer (e.g., assumed subject media and JSON data formatting) and point to that viewer's README for viewer-specific details.

Package

lib-classifier

Linked Issue and/or Talk Post

Closes #6118

How to Review

• Reviewer should confirm that the JSON data format example I removed is in fact not supported (that seems obvious based on Issue Issue with Json data charts Preview #6118) so should be dropped.

Checklist

PR Creator - Please cater the checklist to fit the review needed for your code changes.
PR Reviewer - Use the checklist during your review. Each point should be checkmarked or discussed before PR approval.

General

• Tests are passing locally and on Github
• Documentation is up to date and changelog has been updated if appropriate
• You can yarn panic && yarn bootstrap or docker-compose up --build and FEM works as expected

[coveralls]

coverage: 80.432% (+0.03%) from 80.398%
when pulling 32eacce on edit-scatterplot-readme
into d89db9a on master.

[eatyourgreens]

There’s also issue #5324, since the TESS light curve viewer is technical debt at this point, and TESS subjects can be displayed in the scatter plot viewer.