Fix grammatical errors and introduce app.component() in introduction.md

[seafoamteal]

Description of Problem

Line 55

There are two "the"s missing, one before the word 'counter' and another before the word "rendered".

Line 161

There is an unnecessary comma before the word "too". According to Grammarly, the comma is not needed when the word 'too' is used at the end of the sentence.

Line 223

1. There are two "the"s missing, one before the word "app" and another before the word '"parent's".
2. The word 'objects' is unnecessarily pluralised.
3. The word 'App' is capitalized, even though the variable is named app in every code snippet on the page.

The app.component() method is used out of the blue

The docs say that the way to register a component is to create a new variable and add it to the components option of the parent, but the next code snippet uses the app.component() method without any prior introduction.

Line 305

There is a missing "a" before the word "more".

Proposed Solution

Line 55

Added the missing "the"s.

Line 161

Removed the unneeded comma.

Line 223

Added the two "the"s, made "objects" singular and changed the "A" in "App" to lowercase.

Line 242

Added a small code snippet detailing how to use the app.component() method to register a component.

Line 305

Added the missing "a".

Additional Information

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