feat: add number of posts config for home page (#281)

* Add a SITE config parameter for posts in index page

* docs: update blog post for `postPerIndex` config

---------

Co-authored-by: satnaing <satnaingdev@gmail.com>

src/pages/index.astro

@@ -8,7 +8,7 @@ import Hr from "@components/Hr.astro";
 import Card from "@components/Card";
 import Socials from "@components/Socials.astro";
 import getSortedPosts from "@utils/getSortedPosts";
-import { SOCIALS } from "@config";
+import { SITE, SOCIALS } from "@config";
 
 const posts = await getCollection("blog");
 
@@ -96,7 +96,7 @@ const socialCount = SOCIALS.filter(social => social.active).length;
           <ul>
             {recentPosts.map(
               ({ data, slug }, index) =>
-                index < 4 && (
+                index < SITE.postPerIndex && (
                   <Card
                     href={`/posts/${slug}/`}
                     frontmatter={data}