Use list_objects_v2 in README

[nyoungstudios]

Description of Change

• Updates README documentation to use list_objects_v2 instead of list_objects since that is what the AWS documentation recommends (and list_objects_v2 supports automatic pagination with the client.get_paginator function used in the sample). Should I add a comment or anything in the readme?
• list_objects documentation recommends to use list_objects_v2 documentation

Assumptions

• none

Checklist for All Submissions

• I have added change info to CHANGES.rst
  • Do you want me to add something to the change list for a documentation change?
• If this is resolving an issue (needed so future developers can determine if change is still necessary and under what conditions) (can be provided via link to issue with these details):
  • Detailed description of issue
  • Alternative methods considered (if any)
  • How issue is being resolved
  • How issue can be reproduced
• If this is providing a new feature (can be provided via link to issue with these details):
  • Detailed description of new feature
  • Why needed
  • Alternatives methods considered (if any)

Checklist when updating botocore and/or aiohttp versions

• I have read and followed CONTRIBUTING.rst
• I have updated test_patches.py where/if appropriate (also check if no changes necessary)
• I have ensured that the awscli/boto3 versions match the updated botocore version

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.10%. Comparing base (7432338) to head (89a2089).
Report is 16 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1259      +/-   ##
==========================================
+ Coverage   88.05%   88.10%   +0.05%     
==========================================
  Files          67       67              
  Lines        5904     5904              
==========================================
+ Hits         5199     5202       +3     
+ Misses        705      702       -3     

Flag	Coverage Δ
unittests	88.10% <ø> (+0.05%)	⬆️

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[thehesiod]

list_objects does support pagination as well, we use it in the tests: https://github.com/boto/botocore/blob/08877232170abe910198e3c1f758ae6d0f2df6a0/tests/integration/test_s3.py#L396 but ya I see now that AWS suggests using v2 going forwards, thanks!