Advise how to resolve OkHttp version conflict with Spring Boot

[mthmulders]

Description

Update README with solution for OkHttp version conflict with Spring Boot.

Issue reference

This closes #582.

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation

[codecov]

Codecov Report

Merging #589 (c6b43d0) into master (3c3a527) will decrease coverage by 0.13%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #589      +/-   ##
============================================
- Coverage     77.16%   77.03%   -0.14%     
+ Complexity      942      941       -1     
============================================
  Files            88       88              
  Lines          3009     3009              
  Branches        334      334              
============================================
- Hits           2322     2318       -4     
- Misses          525      528       +3     
- Partials        162      163       +1     

Impacted Files	Coverage Δ
sdk/src/main/java/io/dapr/utils/Retry.java	50.00% <0.00%> (-25.00%)	⬇️

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