chore: add Go icon and fix a command in README

[lym953]

What does this PR do?

In README.md:

1. Add a Go icon which links to the package page on pkg.go.dev
2. fix the Go installation command

Motivation

Testing Guidelines

1. Check the rendered icon in README. It looks good.

   • Click on it. It redirects to the right page.

2. Run the Go installation command. No error.

yiming.luo@COMP-J7WRL6274T go-stack % go get github.com/DataDog/datadog-cdk-constructs-go/ddcdkconstruct
go: downloading github.com/DataDog/datadog-cdk-constructs-go/ddcdkconstruct v1.14.0
go: downloading github.com/DataDog/datadog-cdk-constructs-go v0.0.0-20240813202855-e43af4f7c380
go: upgraded github.com/DataDog/datadog-cdk-constructs-go/ddcdkconstruct v1.13.0 => v1.14.0
yiming.luo@COMP-J7WRL6274T go-stack % 

Additional Notes

Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog

[lym953]

/merge

[dd-devflow]

🚂 MergeQueue: pull request added to the queue

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