README: Expand installation instructions

README.rdoc

@@ -1,12 +1,23 @@
 = sinatra-url-for
 
 <code>sinatra-url-for</code> can be used by a Sinatra application to
-construct absolute paths and full URLs.  For example:
+construct absolute paths and full URLs.
 
+To install it, run:
+
+  sudo gem install emk-sinatra-url-for -s http://gems.github.com
+
+To include it in a Sinatra application, write:
+
+  require 'rubygems'
   gem 'emk-sinatra-url-for'
   require 'sinatra/url_for'
 
-  # From within a request.
+Once this is done, you should be able to call +url_for+ from within a
+request.  Assuming that your application is running on
+<code>example.com</code>, and that it has been mapped to
+<code>/myapp</code>, you should get:
+
   url_for "/"            # Returns "/myapp/"
   url_for "/foo"         # Returns "/myapp/foo"
   url_for "/foo", :full  # Returns "http://example.com/myapp/foo"
@@ -20,7 +31,8 @@ If you're subclassing <code>Sinatra::Base</code>, then you need to call
   end
 
 Thanks to "cypher23" on #mephisto and the folks on #rack for pointing me in
-the right direction.
+the right direction.  If this gem fails to work correctly on your web
+system, please feel free to submit patches and/or bug reports!
 
 == Copyright