fix: rss file path

feat: new rss introduction page

Author: xihale

content/learn/index.smd

@@ -6,7 +6,7 @@
 .alternatives = [{
   .name = "rss",
   .layout = "rss.xml",
-  .output = "/learn/index.xml",
+  .output = "index.xml",
 }],
 .draft = false,
 ---

content/monthly/index.smd

@@ -7,7 +7,7 @@
 .alternatives = [{
   .name = "rss",
   .layout = "rss.xml",
-  .output = "/monthly/index.xml",
+  .output = "index.xml",
 }],
 .custom = {
   .showTocDate = false

content/post/index.smd

@@ -6,11 +6,11 @@
 .alternatives = [{
   .name = "rss",
   .layout = "rss.xml",
-  .output = "/post/index.xml",
+  .output = "index.xml",
 }],
 .draft = false,
 ---
 
 欢迎大家向我们投稿，会同步到微信公众号，投稿方式见[这里](./2023-09-05-hello-world)。
 
-[社区新闻](./news)
+[社区新闻](./news)

content/rss.smd

@@ -0,0 +1,15 @@
+---
+.title = "",
+.date = @date("1990-01-01T00:00:00"),
+.author = "ZigCC",
+.layout = "index.shtml",
+.draft = false,
+---
+
+本站一共有 3 个 RSS 索引，分别索引了 学习、月刊和博客，便于满足不同读者的需求。
+
+他们的链接分别是：
+[/learn/index.xml]($link.page("learn").alternative('rss'))
+[/monthly/index.xml]($link.page("monthly").alternative('rss'))
+[/post/index.xml]($link.page("post").alternative('rss'))
+

layouts/templates/base.shtml

@@ -27,8 +27,8 @@
             <a href="https://github.com/zigcc/zigcc.github.io">Source Code</a>
             |
             <a href="https://creativecommons.org/licenses/by-nc-nd/4.0/">BY-NC-ND 4.0</a>
-            <!-- | -->
-            <!--TODO <a href="/index.xml">RSS</a> --></p>
+            |
+            <a href="/rss">RSS</a></p>
         </div>
         <div>
           <a