Update README to include documentation link

[dyladan]

Short description of the changes

• Update README to point to the newly operational documentation link.
• Update README to keep links in a central location at the bottom
• Update README to differentiate between Application Owners and Library Authors

[OlivierAlbertini]

LGTM

[mayurkale22]

You We should update the documentation link in opentelemetry.io => js => api-reference (https://opentelemetry.io/docs/js/tracing/#api-reference).

[mayurkale22]

I did it here open-telemetry/opentelemetry.io#97 :)

[codecov-io]

Codecov Report

Merging #710 into master will increase coverage by 1.6%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master     #710     +/-   ##
=========================================
+ Coverage   91.03%   92.64%   +1.6%     
=========================================
  Files         224      228      +4     
  Lines       10452    10343    -109     
  Branches      955      941     -14     
=========================================
+ Hits         9515     9582     +67     
+ Misses        937      761    -176

Impacted Files	Coverage Δ
...s/opentelemetry-tracing/src/BasicTracerRegistry.ts	100% <ø> (ø)	⬆️
...lemetry-core/test/trace/globaltracer-utils.test.ts	96.96% <ø> (ø)	⬆️
...-metrics/test/export/ConsoleMetricExporter.test.ts	100% <ø> (ø)	⬆️
...pentelemetry-core/src/metrics/NoopMeterRegistry.ts	100% <100%> (ø)
.../opentelemetry-core/test/metrics/NoopMeter.test.ts	97.29% <100%> (+0.07%)	⬆️
...emetry-exporter-prometheus/test/prometheus.test.ts	98.6% <100%> (ø)	⬆️
packages/opentelemetry-tracing/src/Tracer.ts	98.38% <100%> (-0.03%)	⬇️
...ackages/opentelemetry-metrics/src/MeterRegistry.ts	100% <100%> (ø)
packages/opentelemetry-core/src/trace/NoopSpan.ts	100% <100%> (ø)	⬆️
...s/opentelemetry-metrics/test/MeterRegistry.test.ts	100% <100%> (ø)
... and 61 more