docs: clarify use of ELECTRON_SKIP_BINARY_DOWNLOAD

docs/tutorial/installation.md

@@ -135,14 +135,18 @@ a text file. A typical cache might look like this:
 
 ## Skip binary download
 
-When installing the `electron` NPM package, it automatically downloads the electron binary.
-
-This can sometimes be unnecessary, e.g. in a CI environment, when testing another component.
-
-To prevent the binary from being downloaded when you install all npm dependencies you can set the environment variable `ELECTRON_SKIP_BINARY_DOWNLOAD`.
-E.g.:
-
-```sh
+Under the hood, Electron's JavaScript API binds to a binary that contains its
+implementations. Because this binary is crucial to the function of any Electron app,
+it is downloaded by default in the `postinstall` step every time you install `electron`
+from the npm registry.
+
+However, if you want to install your project's dependencies but don't need to use
+Electron functionality, you can set the `ELECTRON_SKIP_BINARY_DOWNLOAD` environment
+variable to prevent the binary from being downloaded. For instance, this feature can
+be useful in continuous integration environments when running unit tests that mock
+out the `electron` module.
+
+```sh npm2yarn
 ELECTRON_SKIP_BINARY_DOWNLOAD=1 npm install
 ```