chore: update plugin readme with example links

[mayurkale22]

Which problem is this PR solving?

• Include an example link

• Update MySQL readme usage instructions

[codecov-io]

Codecov Report

Merging #647 into master will decrease coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #647      +/-   ##
==========================================
- Coverage   91.42%   91.34%   -0.08%     
==========================================
  Files         195      193       -2     
  Lines       10082     9883     -199     
  Branches      894      891       -3     
==========================================
- Hits         9217     9028     -189     
+ Misses        865      855      -10

Impacted Files	Coverage Δ
...ges/opentelemetry-tracing/src/NoopSpanProcessor.ts	66.66% <0%> (-8.34%)	⬇️
...entelemetry-exporter-jaeger/test/transform.test.ts	100% <0%> (ø)	⬆️
packages/opentelemetry-tracing/src/config.ts	100% <0%> (ø)	⬆️
packages/opentelemetry-tracing/src/utility.ts	100% <0%> (ø)	⬆️
...ges/opentelemetry-exporter-zipkin/src/transform.ts	100% <0%> (ø)	⬆️
packages/opentelemetry-tracing/test/Span.test.ts	100% <0%> (ø)	⬆️
.../opentelemetry-plugin-dns/test/utils/assertSpan.ts	100% <0%> (ø)	⬆️
...ry-tracing/test/export/SimpleSpanProcessor.test.ts	100% <0%> (ø)	⬆️
.../opentelemetry-exporter-zipkin/test/zipkin.test.ts	100% <0%> (ø)	⬆️
.../opentelemetry-exporter-jaeger/test/jaeger.test.ts	100% <0%> (ø)	⬆️
... and 11 more