README: Clarify {{base}} in gopherjs serve. (#741)

Saying "{{base}}.js" might be confusing, so just use the example value
and mention that the .js file name comes from the base directory name.
Hopefully, this is more clear.

Updates #408.

README.md

@@ -35,9 +35,9 @@ For system calls (file system access, etc.), see [this page](https://github.com/
 
 #### gopherjs serve
 
-`gopherjs serve` is a useful command you can use during development. It will start an HTTP server serving on ":8080" by default, and dynamically compile Go packages with GopherJS and serve them.
+`gopherjs serve` is a useful command you can use during development. It will start an HTTP server serving on ":8080" by default, then dynamically compile your Go packages with GopherJS and serve them.
 
-For example, navigating to `http://localhost:8080/example.com/user/project/` should compile and run the Go package `example.com/user/project`. The generated JavaScript output will be served at `http://localhost:8080/example.com/user/project/project.js`. If the directory contains `index.html` it will be served, otherwise a minimal `index.html` that includes `<script src="{{base}}.js"></script>` will be provided, causing the JavaScript to be executed. All other static files will be served too.
+For example, navigating to `http://localhost:8080/example.com/user/project/` should compile and run the Go package `example.com/user/project`. The generated JavaScript output will be served at `http://localhost:8080/example.com/user/project/project.js` (the .js file name will be equal to the base directory name). If the directory contains `index.html` it will be served, otherwise a minimal `index.html` that includes `<script src="project.js"></script>` will be provided, causing the JavaScript to be executed. All other static files will be served too.
 
 Refreshing in the browser will rebuild the served files if needed. Compilation errors will be displayed in terminal, and in browser console. Additionally, it will serve $GOROOT and $GOPATH for sourcemaps.