Update README.md

[gmaciolek]

JIRA Ticket:
bb2-1472

User Story or Bug Summary:

Polish the GitHub SDK repo and readme docs related to Node & Python SDKs. Proof-read and check styling.

What Does This PR Do?

• Simplifies wordy paragraph about access token refresh
• Removes SDK development section

I have gone through and verified that...:

• [x ] This PR is reasonably limited in scope, to help ensure that:
  1. It doesn't unnecessarily tie a bunch of disparate features, fixes, refactorings, etc. together.
  2. There isn't too much of a burden on reviewers.
  3. Any problems it causes have a small "blast radius".
  4. It'll be easier to rollback if that becomes necessary.
• [x ] I have named this PR and its branch such that they'll be automatically be linked to the (most) relevant Jira issue, per: https://confluence.atlassian.com/adminjiracloud/integrating-with-development-tools-776636216.html.
• [x ] This PR includes any required documentation changes, including README updates and changelog / release notes entries.
• All new and modified code is appropriately commented, such that the what and why of its design would be reasonably clear to engineers, preferably ones unfamiliar with the project.
• All tech debt and/or shortcomings introduced by this PR are detailed in TODO and/or FIXME comments, which include a JIRA ticket ID for any items that require urgent attention.
• [ x] Reviews are requested from both:
  • At least two other engineers on this project, at least one of whom is a senior engineer or owns the relevant component(s) here.
  • Any relevant engineers on other projects (e.g. BFD, SLS, etc.).
• Any deviations from the other policies in the DASG Engineering Standards are specifically called out in this PR, above.
  • Please review the standards every few months to ensure you're familiar with them.

[ajshred]

Looks good to me.

[JFU-GIT]

Looks good, thanks for the edits!