Update README.md for Polly.Extensions with telemetry info

[martintmk]

Details on the issue fix or feature implementation

I feel this information should be included here.

Contributes to #1091

Confirm the following

• I started this PR by branching from the head of the default branch
• I have targeted the PR to merge into the default branch
• I have included unit tests for the issue/feature
• I have successfully run a local build

[codecov]

Codecov Report

Merging #1401 (6774fd8) into main (715dbcc) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1401   +/-   ##
=======================================
  Coverage   83.80%   83.80%           
=======================================
  Files         273      273           
  Lines        6476     6476           
  Branches     1010     1010           
=======================================
  Hits         5427     5427           
  Misses        840      840           
  Partials      209      209           

Flag	Coverage Δ
linux	?
macos	83.80% <100.00%> (ø)
windows	83.80% <100.00%> (ø)

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Impacted Files	Coverage Δ
...xtensions/Telemetry/TelemetryResilienceStrategy.cs	100.00% <100.00%> (ø)