Improve disposables docstrings

[ben-grande]

For: QubesOS/qubes-doc#1554
For: QubesOS/qubes-issues#1512

---

When producing the disposable implementation docs](QubesOS/qubes-doc#1554 (comment)), docstrings were missing, so the links were not working.

I did this a bit fast, will do another pass soon.

[ben-grande]

Would be nice if there was an RTD build like for qubes-doc.

[marmarek]

Ignore pylint errors for now, but two other failed jobs are related to your changes.

[marmarek]

PipelineRetry

[marmarek]

Would be nice if there was an RTD build like for qubes-doc.

Not sure if you noticed, but it's here now :)

[marmarek]

Both pylint and mypy complain...

[codecov]

Codecov Report

❌ Patch coverage is 87.80488% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.36%. Comparing base (76b23c9) to head (6bd6093).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
qubes/vm/dispvm.py	88.46%	3 Missing ⚠️
qubes/vm/mix/dvmtemplate.py	92.30%	1 Missing ⚠️
qubes/vm/qubesvm.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #737      +/-   ##
==========================================
+ Coverage   70.34%   70.36%   +0.01%     
==========================================
  Files          61       61              
  Lines       13682    13687       +5     
==========================================
+ Hits         9625     9631       +6     
+ Misses       4057     4056       -1     

Flag	Coverage Δ
unittests	70.36% <87.80%> (+0.01%)	⬆️

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