chore: regenerate README

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Log from Synthtool

2020-12-17 00:52:15,140 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-bigtable/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2020-12-17 00:52:16,111 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

Full log will be available here:
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[yoshi-approver]

Rubber stamped PR!

[igorbernstein2]

Unfortunately this went stale and needs to be rebased

[codecov]

Codecov Report

Merging #579 (b73f575) into master (8240779) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #579      +/-   ##
============================================
- Coverage     81.67%   81.66%   -0.02%     
  Complexity     1151     1151              
============================================
  Files           109      109              
  Lines          7192     7192              
  Branches        376      376              
============================================
- Hits           5874     5873       -1     
- Misses         1118     1120       +2     
+ Partials        200      199       -1     

Impacted Files	Coverage Δ	Complexity Δ
...om/google/cloud/bigtable/emulator/v2/Emulator.java	59.83% <0.00%> (-0.82%)	14.00% <0.00%> (ø%)

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[kolea2]

Unfortunately this went stale and needs to be rebased

@mutianf my latest change to switch to autogenerating the readme (#568) now requires any custom readme content to be added to https://github.com/googleapis/java-bigtable/blob/master/.readme-partials.yml. Can you add your README changes from #557 there instead? This will get things back in sync