chore(docs): reword CSS in JS docs for clarity (#11439)

<!--
  Have any questions? Check out the contributing docs at https://gatsby.app/contribute, or
  ask in this Pull Request and a Gatsby maintainer will be happy to help :)
-->

## Description

Gives clear info about installation of libraries, helpers and gatsby plugins. Adds review comments from emotion docs.

## Related Issues

<!--
  Link to the issue that is fixed by this PR (if there is one)
  e.g. Fixes #1234, Addresses #1234, Related to #1234, etc.
-->

docs/docs/emotion.md

@@ -2,19 +2,19 @@
 title: Emotion
 ---
 
-In this guide, we'll walk through setting up a site with the CSS-in-JS library [Emotion](https://emotion.sh).
+In this guide, you will learn how to set up a site with the CSS-in-JS library [Emotion](https://emotion.sh).
 
 Emotion is a performant and flexible CSS-in-JS library. Building on many other CSS-in-JS libraries, it allows you to style apps quickly with string or object styles. It has predictable composition to avoid specificity issues with CSS. With source maps and labels, Emotion has a great developer experience and great performance with heavy caching in production.
 
-[Server side rendering](https://emotion.sh/docs/ssr) works out of the box in Emotion. We can use React’s `renderToString` or `renderToNodeStream` methods directly without any extra configuration. `extractCritical` feature removes unused rules that were created with emotion and helps loading pages faster.
+[Server side rendering](https://emotion.sh/docs/ssr) works out of the box in Emotion. You can use React’s `renderToString` or `renderToNodeStream` methods directly without any extra configuration. `extractCritical` feature removes unused rules that were created with emotion and helps loading pages faster.
 
 First, open a new terminal window and run the following to create a new site:
 
 ```shell
 npx gatsby new emotion-tutorial https://github.com/gatsbyjs/gatsby-starter-hello-world
 ```
 
-Second, we'll install the necessary dependencies for Emotion and Gatsby.
+Second, install the necessary dependencies for Emotion and Gatsby.
 
 ```shell
 npm install --save gatsby-plugin-emotion @emotion/core @emotion/styled

docs/docs/glamor.md

@@ -2,7 +2,7 @@
 title: Glamor
 ---
 
-In this guide, we'll walk through setting up a site with the CSS-in-JS library [Glamor](https://github.com/threepointone/glamor).
+In this guide, you will learn setting up a site with the CSS-in-JS library [Glamor](https://github.com/threepointone/glamor).
 
 Glamor is not actively maintained, the maintainer recommends using [Emotion](/docs/emotion).
 
@@ -19,7 +19,7 @@ First, open a new terminal window and run the following to create a new site:
 npx gatsby new glamor-tutorial https://github.com/gatsbyjs/gatsby-starter-hello-world
 ```
 
-Second, install the Gatsby plugin for Glamor.
+Second, install the necessary dependencies for Glamor and Gatsby.
 
 ```shell
 npm install --save gatsby-plugin-glamor glamor

docs/docs/styled-components.md

@@ -2,7 +2,7 @@
 title: Styled Components
 ---
 
-In this guide, we'll walk through setting up a site with the CSS-in-JS library [Styled Components](https://www.styled-components.com/).
+In this guide, you will learn setting up a site with the CSS-in-JS library [Styled Components](https://www.styled-components.com/).
 
 Styled Components lets you use actual CSS syntax inside your components. Styled Components is a variant on "CSS-in-JS"—which solves many of the problems with traditional CSS.
 
@@ -20,7 +20,7 @@ First, open a new terminal window and run the following to create a new site:
 npx gatsby new styled-components-tutorial https://github.com/gatsbyjs/gatsby-starter-hello-world
 ```
 
-Next, we'll install the necessary dependencies for `styled-components`, including the Gatsby plugin.
+Second, install the necessary dependencies for `styled-components`, including the Gatsby plugin.
 
 ```shell
 npm install --save gatsby-plugin-styled-components styled-components babel-plugin-styled-components