web: quick-start install cmd -> /download/install.sh + fix docs crumb title

- index.md (快速开始) one-line install now uses
  https://pmm.parlz.com/download/install.sh (matches the download folder).
- docs/index.php: read the crumb title from the raw markdown's first '# ' line
  (was reading the rendered body, which had already converted '#' to <h1>, so it
  fell back to the slug e.g. 'index').

web/docs/index.php

@@ -63,15 +63,15 @@ function render_tree(string $dir, string $rel): string {
 }
 
 $body = '';
+$title = $page;
 $f = $mdDir . '/' . $page . '.md';
 if (is_file($f)) {
     $raw = (string)file_get_contents($f);
     $raw = str_replace("\r", "", $raw);
+    /* title = first '# ' line of the raw markdown (not the rendered body) */
+    if (preg_match('/^#\s+(.+)$/m', $raw, $m)) $title = trim($m[1]);
     $body = md($raw);
 }
-// crumb title = file's first heading or slug
-$title = $page;
-if ($body !== '' && preg_match('/^#\s+(.+)$/m', str_replace('<', '', $body), $m)) $title = trim(strip_tags($m[1]));
 
 if (isset($_GET['ajax'])) {   /* partial response for AJAX nav (no layout) */
     echo '<div class="docs-crumb">文档 / ' . htmlspecialchars($title) . '</div>';

web/docs/md/index.md

@@ -7,7 +7,7 @@
 ## 一分钟装好
 
 ```bash
-curl -sSL https://pmm.parlz.com/install.sh | bash
+curl -sSL https://pmm.parlz.com/download/install.sh | bash
 ```
 
 装好后：