docs: fix minor grammar (#11766)

Co-authored-by: Joshua Chen <sidachen2003@gmail.com>

Author: work109677-sudo

website/docs/installation.mdx

@@ -101,7 +101,7 @@ my-website
   - `/src/pages` - Any JSX/TSX/MDX file within this directory will be converted into a website page. More details can be found in the [pages guide](guides/creating-pages.mdx)
 - `/static/` - Static directory. Any contents inside here will be copied into the root of the final `build` directory
 - `/docusaurus.config.js` - A config file containing the site configuration. This is the equivalent of `siteConfig.js` in Docusaurus v1
-- `/package.json` - A Docusaurus website is a React app. You can install and use any npm packages you like in them
+- `/package.json` - A Docusaurus website is a React app. You can install and use any npm packages you like in it.
 - `/sidebars.js` - Used by the documentation to specify the order of documents in the sidebar
 
 ### Monorepos {#monorepos}
@@ -141,7 +141,7 @@ Congratulations! You have just created your first Docusaurus site! Browse around
 
 ## Build {#build}
 
-Docusaurus is a modern static website generator so we need to build the website into a directory of static contents and put it on a web server so that it can be viewed. To build the website:
+Docusaurus is a modern static website generator, so we need to build the website into a directory of static contents and put it on a web server so that it can be viewed. To build the website:
 
 ```bash npm2yarn
 npm run build