README.md: rename the duplicate "Introduction" to "Getting Started" (nvim-lua#572)

Changing this second "Introduction" heading to "Getting Started"
The recent change in README which moved the youtube link from FAQ
to it's own section used the heading "Introduction" which is already
the first heading in the file.

Author: restray

README.md

@@ -71,9 +71,9 @@ If you would prefer to hide this step and run the plugin sync from the command l
 nvim --headless "+Lazy! sync" +qa
 ```
 
-### Introduction
+### Getting Started
 
-To get started, see [Effective Neovim: Instant IDE](https://youtu.be/stqUbv-5u2s), covering the previous version. Note: The install via init.lua is outdated, please follow the install instructions in this file instead. An updated video is coming soon.
+See [Effective Neovim: Instant IDE](https://youtu.be/stqUbv-5u2s), covering the previous version. Note: The install via init.lua is outdated, please follow the install instructions in this file instead. An updated video is coming soon.
 
 ### Recommended Steps