[getting-started.md] fixes for English grammar and flow

[glenn-slayden]

documentation

Please check the type of change your PR introduces:

• [ ] Update
• [ ] Bugfix
• [ ] Feature
• [ ] Code style update (formatting, renaming)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [x] Documentation content changes

What is the current behavior?

English grammar errors, style and flow.

Issue Number: N/A

What is the new behavior?

fixed.

Other information