doc: improve paragraph in esm.md

Edit for clarity, correct tense, and brevity.

PR-URL: #34064
Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/api/esm.md

@@ -124,12 +124,12 @@ as ES modules and `.cjs` files are always treated as CommonJS.
 ### Package scope and file extensions
 
 A folder containing a `package.json` file, and all subfolders below that folder
-down until the next folder containing another `package.json`, is considered a
-_package scope_. The `"type"` field defines how `.js` files should be treated
-within a particular `package.json` file’s package scope. Every package in a
+until the next folder containing another `package.json`, are a
+_package scope_. The `"type"` field defines how to treat `.js` files
+within the package scope. Every package in a
 project’s `node_modules` folder contains its own `package.json` file, so each
-project’s dependencies have their own package scopes. A `package.json` lacking a
-`"type"` field is treated as if it contained `"type": "commonjs"`.
+project’s dependencies have their own package scopes. If a `package.json` file
+does not have a `"type"` field, the default `"type"` is `"commonjs"`.
 
 The package scope applies not only to initial entry points (`node my-app.js`)
 but also to files referenced by `import` statements and `import()` expressions.