docs: add challenge admonition (#2075)

add challenge admonition to development page
fix frontmatter in development page

Author: TC-MO

sources/platform/actors/development/index.md

@@ -1,6 +1,6 @@
 ---
 title: Actor development
-desc: Read about the technical part of building Apify Actors. Learn to define Actor inputs, build new versions, persist Actor state, and choose base Docker images.
+description: Read about the technical part of building Apify Actors. Learn to define Actor inputs, build new versions, persist Actor state, and choose base Docker images.
 sidebar_label: Development
 sidebar_position: 7.4
 slug: /actors/development
@@ -10,6 +10,14 @@ slug: /actors/development
 
 ---
 
+:::note Join The Apify $1M Challenge
+
+Build and publish new tools on Apify and have multiple chances to win big prizes.
+
+[Join the challenge now.](https://apify.com/challenge)
+
+:::
+
 This section will guide you through the whole story of [Actor](../index.mdx) development.
 
 You can follow chapters sequentially from [Quick start](/platform/actors/development/quick-start), where you learn how to create your first Actor in just a few minutes, through the more technical sections describing the whole Actor model, up to the [Performance](/sources/platform/actors/development/performance.md) section, where you learn how to fine-tune your Actor to get the most out of the Apify platform.