Clarify documentation in README.txt

Some of the existing documentation is unclear. For example:

 #1) Attach popup behavior to a link with popups_add_popups() call.
  ----------------------------------------------------------------  
  <!-- In html or theme -->
  <a href="popups/test/response" id="mylink"> 
  <a href="popups/test/response" id="mylink2"> 
  
  // In your module
  popups_add_popups(array('#mylink', '#mylink2=>array('width'=>'200px')));  
...

What module are you referring to? Where is that function supposed to be? Does it have to be in a custom module, or can it run in template.php?
Do you always need 2 links? Do they have to be in some piece of dynamic content (like a node) or can they be in a theme template?

The documentation lists 4 methods of implementing this API, but the descriptions of usage are too vague. Example:

  Example in code:
    popups_add_popups();
    $output .= l("Pop up entire local page.", 'popups/test/response', array('attributes'=>array('class' => 'popups')));

Instructions such as this do not describe where this snippet of code needs to run. Does is need to be in a custom module? Does it need to be called as part of a function? Can it run in a tpl.php file? Can it run in template.php?

I've also enabled the "Popups: Test Page" module, but the URL for that test page is not in the documentation. It seems like the URL is probably yourdomain.com/popups/test/response, but the "Hello world" text I see on that page doesn't describe what behavior I should expect to see on that page. It would be nice if the path to this page was in the description of the module itself, or had an admin menu link. At the very least, it should be listed in the README.txt with a description of the what to expect.