Update readmes for mavenCentral

[RHenigan]

This PR is ready for review.

Risk

This PR makes no API changes.

Testing Plan

• I have verified that I have not introduced new warnings in this PR (or explain why below)
• I have run the unit tests with this PR
• I have tested this PR against Core and verified behavior (if applicable, if not applicable, explain why below).
• I have tested Android, Java SE, and Java EE

Unit Tests

N/A

Core Tests

N/A

Summary

Update READMEs to use mavenCentral repository and version 5.1

CLA

• I have signed the CLA

[codecov]

Codecov Report

Merging #1657 (30e35a4) into release/5.1.0_RC (e6e61be) will increase coverage by 0.00%.
The diff coverage is n/a.

❗ Current head 30e35a4 differs from pull request most recent head 64c5e8a. Consider uploading reports for the commit 64c5e8a to get more accurate results

@@                 Coverage Diff                 @@
##             release/5.1.0_RC    #1657   +/-   ##
===================================================
  Coverage               54.00%   54.00%           
- Complexity               5305     5306    +1     
===================================================
  Files                     555      555           
  Lines                   24532    24532           
  Branches                 3094     3094           
===================================================
+ Hits                    13248    13249    +1     
  Misses                  10132    10132           
+ Partials                 1152     1151    -1     

Impacted Files	Coverage Δ	Complexity Δ
...smartdevicelink/encoder/VirtualDisplayEncoder.java	44.40% <0.00%> (-0.70%)	9.00% <0.00%> (ø%)
...rtdevicelink/streaming/video/SdlRemoteDisplay.java	51.21% <0.00%> (+1.21%)	5.00% <0.00%> (ø%)
...nk/managers/audio/AudioDecoderCompatOperation.java	79.54% <0.00%> (+4.54%)	10.00% <0.00%> (+1.00%)