Add Tembo to README

[AlekSi]

https://tembo.io/docs/tembo-stacks/mongo-alternative

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.80%. Comparing base (a8fc642) to head (ef50188).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4168      +/-   ##
==========================================
- Coverage   74.34%   73.80%   -0.54%     
==========================================
  Files         354      354              
  Lines       23013    23013              
==========================================
- Hits        17108    16985     -123     
- Misses       4590     4729     +139     
+ Partials     1315     1299      -16     

see 11 files with indirect coverage changes

Flag	Coverage Δ
filter-true	66.72% <ø> (-0.63%)	⬇️
hana-1	?
integration	66.72% <ø> (-0.63%)	⬇️
mongodb-1	4.81% <ø> (+<0.01%)	⬆️
postgresql-1	48.77% <ø> (+0.06%)	⬆️
postgresql-2	49.18% <ø> (-0.03%)	⬇️
postgresql-3	46.27% <ø> (-0.02%)	⬇️
sqlite-1	47.89% <ø> (-0.08%)	⬇️
sqlite-2	48.34% <ø> (-0.04%)	⬇️
sqlite-3	45.36% <ø> (ø)
unit	32.92% <ø> (ø)

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