create-promotion (#512)

docs/build/dapp-staking/for-devs/create-promotion.md

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+---
+sidebar_position: 4
+---
+
+# Create a promotion card on top page
+
+If you have a campaign or new product you would like to share in the community, this will help you to spread the news. It will create a card which will be shown on dApp Staking top page as well as Portal asset page.
+
+You can create a PR reguraly but once evry month at most.
+
+![promotion-card](img/promotion-card.png)
+
+# Steps on creating a PR for the promotion card
+
+- Find a file [dapp_promotion.json](https://github.com/AstarNetwork/astar-apps/blob/bd689c35347c47e9287039b74ae60ca4035378fa/src/data/dapp_promotions.json).
+
+- Create a PR to <code>release-hotfix</code> branch in [astar-apps](https://github.com/AstarNetwork/astar-apps).
+
+
+:::info
+- **Image must be 16:9 and recommended size is less than 1MG**.
+- **Description has to be within 65 characters**.
+- Your PR will be merged after being reviewed by dApp Staking operation team.
+- Card will be removed at anytime when the operation team decided to do so.
+- Multiple PRs or more than one PR with in a month from the same team will not be approved.
+:::
+