change wording slightly to reflect what is actually happening there

The `npm install . -g` command here doesn't actually allow you to `require ('myfancymodule')`. It does tell you though if the npm build worked. This was confusing to me today when I built my first npm package. I figured I would change the wording slightly, and I notice that this text is repeated a bunch of places:

```
fetch:npm-www jane$ grep -r 'npm install . -g' .
./doc/developers.html:<pre><code>npm install . -g
./doc/misc/npm-developers.html:<pre><code>npm install . -g
./node_modules/npm/doc/misc/npm-developers.md:    npm install . -g
./node_modules/npm/html/doc/misc/npm-developers.html:<pre><code>npm install . -g</code></pre>
```

My assumption is that the html documents are generated off the markdown document, but it's not clear from the `npm-www` documentation where that process happens. So I frobbed the markdown doc; I'm happy to "fix" the other places it occurs as well, but I wasn't sure whether that was the correct path.