update aws xray receiver readme

[JohnWu20]

Update the aws xray receiver readme. Fix an error for the config file part.

[codecov]

Codecov Report

Merging #1485 into master will increase coverage by 1.35%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1485      +/-   ##
==========================================
+ Coverage   87.36%   88.71%   +1.35%     
==========================================
  Files         343      344       +1     
  Lines       16775    16851      +76     
==========================================
+ Hits        14656    14950     +294     
+ Misses       1663     1435     -228     
- Partials      456      466      +10     

Flag	Coverage Δ
integration	70.80% <ø> (?)
unit	87.36% <ø> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...eiver/awsxrayreceiver/internal/udppoller/poller.go	97.61% <0.00%> (-2.39%)	⬇️
internal/common/testing/container/container.go	73.68% <0.00%> (ø)
receiver/carbonreceiver/transport/tcp_server.go	66.33% <0.00%> (+0.99%)	⬆️
receiver/jmxreceiver/receiver.go	94.73% <0.00%> (+10.52%)	⬆️
receiver/dockerstatsreceiver/docker.go	92.30% <0.00%> (+39.05%)	⬆️
receiver/dockerstatsreceiver/receiver.go	96.82% <0.00%> (+49.20%)	⬆️
receiver/jmxreceiver/subprocess/subprocess.go	96.52% <0.00%> (+73.61%)	⬆️
receiver/redisreceiver/receiver.go	87.50% <0.00%> (+87.50%)	⬆️
receiver/redisreceiver/client.go	100.00% <0.00%> (+100.00%)	⬆️
receiver/redisreceiver/factory.go	100.00% <0.00%> (+100.00%)	⬆️
... and 1 more

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