docs(guides): use npx in getting-started (#1708)

Keep the mention the webpack binary's path but use the `npx` utility
now that it ships with Node. Fix some punctuation and grammar. Clarify 
why npm scripts are still useful even over `npx`.

Author: MajorBreakfast

src/content/guides/getting-started.md

@@ -141,10 +141,10 @@ __dist/index.html__
 
 In this setup, `index.js` explicitly requires `lodash` to be present, and binds it as `_` (no global scope pollution). By stating what dependencies a module needs, webpack can use this information to build a dependency graph. It then uses the graph to generate an optimized bundle where scripts will be executed in the correct order.
 
-With that said, let's run `webpack` with our script as the [entry point](/concepts/entry-points) and `bundle.js` as the [output](/concepts/output):
+With that said, let's run `npx webpack` with our script as the [entry point](/concepts/entry-points) and `bundle.js` as the [output](/concepts/output). The `npx` command, which ships with Node 8.2 or higher, runs the webpack binary (`./node_modules/.bin/webpack`) of the webpack package we installed in the beginning:
 
 ``` bash
-./node_modules/.bin/webpack src/index.js dist/bundle.js
+npx webpack src/index.js dist/bundle.js
 
 Hash: ff6c1d39b26f89b3b7bb
 Version: webpack 2.2.0
@@ -204,7 +204,7 @@ module.exports = {
 Now, let's run the build again but instead using our new configuration:
 
 ``` bash
-./node_modules/.bin/webpack --config webpack.config.js
+npx webpack --config webpack.config.js
 
 Hash: ff6c1d39b26f89b3b7bb
 Version: webpack 2.2.0
@@ -240,7 +240,7 @@ __package.json__
 }
 ```
 
-Now the `npm run build` command can be used in place of the longer commands we used earlier. Note that within `scripts` we can reference locally installed npm packages by name instead of writing out the entire path. This convention is the standard in most npm-based projects and allows us to directly call `webpack`, instead of `./node_modules/.bin/webpack`
+Now the `npm run build` command can be used in place of the `npx` command we used earlier. Note that within `scripts` we can reference locally installed npm packages by name the same way we did with `npx`. This convention is the standard in most npm-based projects because it allows all contributors to use the same set of common scripts (each with flags like `--config` if necessary).
 
 Now run the following command and see if your script alias works: