Clarify tooltip for WCS panzoom tool

[pllim]

Based on Imviz Hack Hour feedback. This goes with glue-viz/glue-jupyter#245

[codecov]

Codecov Report

Merging #749 (b11650a) into main (e29b827) will decrease coverage by 0.16%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #749      +/-   ##
==========================================
- Coverage   63.00%   62.84%   -0.17%     
==========================================
  Files          65       65              
  Lines        4290     4290              
==========================================
- Hits         2703     2696       -7     
- Misses       1587     1594       +7     

Impacted Files	Coverage Δ
jdaviz/configs/imviz/plugins/tools.py	37.62% <100.00%> (ø)
...configs/default/plugins/data_tools/file_chooser.py	65.71% <0.00%> (-3.43%)	⬇️
jdaviz/configs/imviz/helper.py	98.49% <0.00%> (-0.51%)	⬇️
jdaviz/configs/specviz/plugins/viewers.py	60.94% <0.00%> (ø)

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[camipacifici]

I am happy with the change. Thank you!