Add docs for security models (#9)

- Change default security to CONFIGURE_ME
- Fix log on return URL handling
- Update INSTALLING security model descriptions

src/public/docs/the-cli.php

@@ -0,0 +1,24 @@
+<?php
+include '../../start.php';
+
+$db = Data::getConnection();
+Security::verifyUser($db, redirectIfAnonymous: false);
+
+page_head('About the CLI | Documentation'); ?>
+<h1>About the CLI</h1>
+<p class=back-link><a href=./>&lang;&lang; Documentation Home</a>
+<article class=docs>
+    <p>Feed Reader Central&rsquo;s low-friction design includes having many administrative tasks run in a terminal or
+        shell. &ldquo;CLI&rdquo; is short for &ldquo;Command Line Interface&rdquo;, and refers to commands that are run
+        via PHP&rsquo;s <code>php-cli</code> command. Ensure that the version of PHP installed also has that feature
+        enabled. (If you are using the recommended
+        <a href=https://frankenphp.dev target=_blank rel=noopener>FrankenPHP</a> environment, it has PHP CLI support;
+        use <code>frankenphp php-cli</code> instead of <code>php-cli</code> when following instructions here.)
+    <h2>Running CLI Commands</h2>
+    <p>CLI commands should be run from the same directory with <code>start.php</code>; this will be one directory level
+        up from <code>/public</code>, the web root directory. CLI utilities are in the <code>/util</code> directory, so
+        an invocation will follow the pattern:
+    <p><code>php-cli util/some-process.php command option1 option2</code>
+</article><?php
+page_foot();
+$db->close();