Include the new step 2 of installation, starting the program with `brew
services`.

After the license has been added, the daemon must be restarted in order
for the license to be recognised.

License the software with the GNU AGPLv3+ with the exception of the
'aquatic-prime' and 'paddle' libraries and 'aquatic-prime' binary, which
are licensed under the GNU GPLv3+.

Forgot to change this when I changed the function signature.

For whatever reason, the environment variables in my `.htaccess` weren't
getting passed to my FastCGI executables on my production server.

Wasn't sure how to get them passed to the programs, so decided instead
to compile the env variables into the binaries.

To do that, we source the environment file before building the release
builds in the Docker container.

Renames the binary. The name "license-generator" no longer seems apt at
this point. That binary doesn't actually generate a license, it serves
as the webhook endpoint for Paddle's license fulfillment. Our `license`
binary handles the actual license generation.

The URL I'll be using for the webhook is `/fulfillment`, so this also
makes sense from that perspective.

Add the instructions we put in the fulfillment email to the
thank-you/license download page. Want to make sure buyers know how to
license the software after purchasing it.

Rephrase the install text to be simpler and more to the point.

Include install and license instructions in the purchase fulfillment
email.

Paddle will take the text from the response of this endpoint and include
it in the purchase fulfillment email to a customer.

Include the URL for the purchaser to download their license. Use the
'url' crate's parser to build the URL in order to URL-escape special
characters.

Honestly I'd rather have had a system where the license file gets
included in the receipt email. Unfortunately, with the Paddle
fulfillment mechanism I'm using, we can only send text. I learned after
building the download endpoint that I could manage fulfillment myself.
This would require me to listen to an "alert"-type Paddle webhook, and
send the email myself (which would include the license file). Since I
already built the license download page, I decided to just use it
instead of doing the emailing. Also, my web host limits my SMTP usage,
so there could be issues there. I'd have to do the emailing in a
separate batch process instead of in the webhook handler to ensure that
no emails would get dropped.

Move the existing thank-you page to `thank-you-license-download.html`.

Use `thank-you.html` as the final page of the purchase flow. Paddle will
redirect to this page at the end of purchase. Allows us to retain some
branding during purchase.

Using the existing HTML file for a better URL.

Done already.