chore: regenerate README

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Log from Synthtool

2020-11-17 09:41:32,582 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-spanner/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working directory clean
2020-11-17 09:41:33,601 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

Full log will be available here:
https://source.cloud.google.com/results/invocations/005ecbdd-e849-49dc-b49e-0b895e2d2872/targets

• To automatically regenerate this PR, check this box.

[yoshi-approver]

Rubber stamped PR!

[codecov]

Codecov Report

Merging #640 (0865466) into master (54de514) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #640   +/-   ##
=========================================
  Coverage     84.04%   84.04%           
  Complexity     2503     2503           
=========================================
  Files           141      141           
  Lines         13810    13810           
  Branches       1318     1318           
=========================================
  Hits          11607    11607           
  Misses         1657     1657           
  Partials        546      546           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 54de514...0865466. Read the comment docs.