Added limitation in ot-shim readme

[mercybassey]

Which problem is this PR solving?

This PR informs users that the OpenTracing shim doesn't include a scope manager.

Fixes #2700

Short description of the changes

This PR updates the OpenTracing shim Readme.md file by adding a limitation section; informing users that the OpenTracing shim doesn't include a scope manager.

Type of change

• This change requires a documentation update

How Has This Been Tested?

No test was created/run

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[mercybassey]

Hi @pichlermarc I'd appreciate your review. Thanks.

[pichlermarc]

thanks for working on this - a few suggestions as per my understanding of the issue.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.27%. Comparing base (7ed67f9) to head (b6b06a1).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5072      +/-   ##
==========================================
+ Coverage   93.26%   93.27%   +0.01%     
==========================================
  Files         317      317              
  Lines        8195     8195              
  Branches     1641     1641              
==========================================
+ Hits         7643     7644       +1     
+ Misses        552      551       -1     

see 1 file with indirect coverage changes

[mercybassey]

thanks for working on this - a few suggestions as per my understanding of the issue.

@pichlermarc I have committed your suggestions. Thanks.