fix: joss reviews

[dirmeier]

Addresses several JOSS review items.

• Upgrades dependency versions README quickstart fails on a pip install: dependency bounds resolve an untested combination #73
• Fixes code coverage Missing coverage data: pytest addopts uses --cov=sabc, so coverage collects no data #74
• Fixes unit tests when jrnmm is not available Test collection aborts on a base install (--doctest-modules imports the optional jrnmm) #75
• • Removes the reference to the non-existent Makefile Contributing docs reference make tests / make lints but there is no root Makefile #76.
• Fixes notebook issues after upgrade to v0.4.0 [JOSS REVIEW] "Getting started" example throws an error. #77, [JOSS REVIEW] "More detailed intro" example throws an error #78
• Adds a Workflow section to the README and landing page [JOSS REVIEW] More pedagogical examples in docs #83.
• Expands the notebooks with text between code cells explaining what each
  choice does and why [JOSS REVIEW] More pedagogical examples in docs #83.
• Adds a Contributing and Support section No documented support channel #87

[codecov]

Codecov Report

❌ Patch coverage is 92.30769% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.00%. Comparing base (335bd17) to head (49293e7).
⚠️ Report is 31 commits behind head on main.

Files with missing lines	Patch %	Lines
sbijax/_src/conftest.py	50.00%	2 Missing ⚠️
sbijax/_src/simulators/conftest.py	71.42%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main      #86       +/-   ##
===========================================
+ Coverage   80.92%   93.00%   +12.08%     
===========================================
  Files          45       99       +54     
  Lines        1814     2817     +1003     
===========================================
+ Hits         1468     2620     +1152     
+ Misses        346      197      -149     

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