Clean up README.md

[compulim]

Describe the bug

Things to clean up in README.md and CHANGELOG.md before release. Please add to this list if something come up in your mind.

Since the clean up could be big and potentially conflicting with all incoming PRs, so make it just before release will ease our burden on merging PRs.

• *: Microsoft organization name change
  • https://github.com/Microsoft/BotFramework-WebChat should become https://github.com/microsoft/BotFramework-WebChat
  • Our organization name changed to lowercase
• CHANGELOG.md: "Update Japanese locale to" or "Update Japanese to"
  • We have mixed use of "Update XXX locale to", and "Update XXX to"
• Typo for CHANGELOG.md
  • sip to SIP or sip:
  • "AdaptiveCards" to "Adaptive Cards"
• Typo for 19.a/README.md line 138
  • Add a note for PROXY_BOT_URL
    • "To enable this feature, add PROXY_BOT_URL=http://localhost:3978 to /web/.env"
    • This note can be found in other samples (19.b and 20.a)

Addendum for typos for CHANGELOG.md

• Fix #1980. Changed sendBoxTextArea styles to break words longer than the <textarea>, by @tdurnford in PR #1986
• Fix #1429. Changed Markdown-It options to render newline characters correctly, by @tdurnford in PR #1988

[Bug]

[corinagum]

Almost ready to start work on this one - just waiting for 2 more PR's to be merged in.

[corinagum]

Not sure what your fix is for #1429 (last item)