DOCS: Update cubeviz slice docs

[javerbukh]

Description

This pull request is to address the changed UI since these docs were made and add some more context on toolbar interactions with the slice tool.

Checklist for package maintainer(s)

This checklist is meant to remind the package maintainer(s) who will review this pull request of some common things to look for. This list is not exhaustive.

• Are two approvals required? Branch protection rule does not check for the second approval. If a second approval is not necessary, please apply the trivial label.
• Do the proposed changes actually accomplish desired goals? Also manually run the affected example notebooks, if necessary.
• Do the proposed changes follow the STScI Style Guides?
• Are tests added/updated as required? If so, do they follow the STScI Style Guides?
• Are docs added/updated as required? If so, do they follow the STScI Style Guides?
• Did the CI pass? If not, are the failures related?
• Is a change log needed? If yes, is it added to CHANGES.rst?
• Is a milestone set? Milestone is only currently required for PRs related to Imviz MVP.
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[codecov]

Codecov Report

Merging #1158 (be36be7) into main (b1f1748) will decrease coverage by 0.75%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1158      +/-   ##
==========================================
- Coverage   76.86%   76.10%   -0.76%     
==========================================
  Files          87       87              
  Lines        6661     6667       +6     
==========================================
- Hits         5120     5074      -46     
- Misses       1541     1593      +52     

Impacted Files	Coverage Δ
jdaviz/configs/imviz/wcs_utils.py	66.66% <0.00%> (-26.67%)	⬇️
jdaviz/configs/imviz/plugins/compass/compass.py	85.00% <0.00%> (-12.50%)	⬇️
jdaviz/configs/imviz/plugins/viewers.py	74.12% <0.00%> (-9.10%)	⬇️
...configs/default/plugins/data_tools/file_chooser.py	65.71% <0.00%> (-3.43%)	⬇️
...igs/specviz/plugins/line_analysis/line_analysis.py	84.76% <0.00%> (-0.49%)	⬇️
jdaviz/core/template_mixin.py	100.00% <0.00%> (ø)
jdaviz/core/registries.py	79.68% <0.00%> (+0.65%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b1f1748...be36be7. Read the comment docs.

[pllim]

Maybe it is best if @kecnry can look at this since he implemented this feature.

[kecnry]

right now this is technically true, but will change slightly if/when #1115 is merged. Maybe it would be simpler to just skip this part about deselecting, etc, and say "When the slice to is active, clicking anywhere on the spectrum viewer will select the nearest slice across all viewers, even if the indicator is off-screen"? The underlying logic for "defaulting" tools is somewhat complex to explain in words, but I think is intuitive and quickly learned just by using it 🤞

[javerbukh]

Sounds good, I updated the text in the latest commit. Thanks!