feat: document set dundermethod add and iadd

[florian-hoenicke]

No description provided.

[github-actions]

Latency summary

Current PR yields:

• 😶 index QPS at 1763, delta to last 3 avg.: +0%
• 😶 query QPS at 27, delta to last 3 avg.: -2%

Breakdown

Version	Index QPS	Query QPS
current	1763	27
0.8.16	1772	27
0.8.15	1768	28
0.8.14	1700	27

Backed by latency-tracking. Further commits will update this comment.

[codecov]

Codecov Report

Merging #1555 (f09fa5f) into master (228d317) will increase coverage by 0.31%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1555      +/-   ##
==========================================
+ Coverage   84.55%   84.87%   +0.31%     
==========================================
  Files         109      109              
  Lines        6417     6485      +68     
==========================================
+ Hits         5426     5504      +78     
+ Misses        991      981      -10     

Impacted Files	Coverage Δ
jina/types/sets/document.py	96.15% <100.00%> (+0.45%)	⬆️
jina/logging/profile.py	68.33% <0.00%> (-0.58%)	⬇️
jina/drivers/craft.py	100.00% <0.00%> (ø)
jina/types/ndarray/generic.py	100.00% <0.00%> (ø)
jina/drivers/encode.py	94.91% <0.00%> (+0.08%)	⬆️
jina/jaml/__init__.py	95.93% <0.00%> (+0.09%)	⬆️
jina/enums.py	96.52% <0.00%> (+0.09%)	⬆️
jina/peapods/peas/gateway/rest/__init__.py	94.00% <0.00%> (+0.12%)	⬆️
jina/executors/indexers/crud_vector.py	93.51% <0.00%> (+0.18%)	⬆️
jina/executors/indexers/vector.py	88.02% <0.00%> (+0.29%)	⬆️
... and 14 more

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