Fix broken markdown link for Anthropic billing settings (#7589)

Co-authored-by: openhands <[email protected]>

Author: mkusaka

docs/modules/usage/installation.mdx

@@ -95,7 +95,7 @@ OpenHands requires an API key to access most language models. Here's how to get
 
 1. [Create an Anthropic account](https://console.anthropic.com/)
 2. [Generate an API key](https://console.anthropic.com/settings/keys)
-3. [Set up billing(https://console.anthropic.com/settings/billing)
+3. [Set up billing](https://console.anthropic.com/settings/billing)
 
 Consider setting usage limits to control costs.