Update README.md cloud link (#40692)

Updated the cloud sign-up link to point to new cloud (billing) edition.

## Description
> [!TIP]  
> _Add a TL;DR when the description is longer than 500 words or
extremely technical (helps the content, marketing, and DevRel team)._
>
> _Please also include relevant motivation and context. List any
dependencies that are required for this change. Add links to Notion,
Figma or any other documents that might be relevant to the PR._


Fixes #`Issue Number`  
_or_  
Fixes `Issue URL`
> [!WARNING]  
> _If no issue exists, please create an issue first, and check with the
maintainers if the issue is valid._

## Automation

/ok-to-test tags=""

### 🔍 Cypress test results
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> [!CAUTION]  
> If you modify the content in this section, you are likely to disrupt
the CI result for your PR.

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## Communication
Should the DevRel and Marketing teams inform users about this change?
- [ ] Yes
- [ ] No


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Documentation**
- Updated the signup link in the README to use the new Appsmith Cloud
URL.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

README.md

@@ -33,7 +33,7 @@ Organizations build custom applications like dashboards, admin panels, customer
 ## Installation
 There are two ways to start using Appsmith:
 
-- Signup on [Appsmith Cloud](https://app.appsmith.com/?utm_source=github&utm_medium=organic&utm_campaign=readme).
+- Signup on [Appsmith Cloud](https://login.appsmith.com/?utm_source=github&utm_medium=organic&utm_campaign=readme).
 - Install Appsmith on your machine. See the installation guides below. 
 
 | Installation Methods                                                                                                            | Documentation                                                                                                                                                    |