Fix Go example link in CDP SDK docs

[0x4tl4nt]

Description

The docs previously referenced a non-existent file example.go for a full end-to-end example of using the CDP SDK:

I tried to find it in other dirs, assuming that the file existed.
The previous link can be confusing for users because it suggests a single file example (example.go) that isn’t in the repo.
After searching, I decided to change the suggestion itself and add a link to the existing directory with all the examples:

• See example.go for an end-to-end example of how to use the CDP SDK. > See the Go examples directory in the CDP SDK repository for runnable end‑to‑end usage examples.
• https://github.com/coinbase/cdp-sdk/tree/main/examples/go/example.go > https://github.com/coinbase/cdp-sdk/tree/main/examples/go/

Tests

Verified that the link works and leads to runnable Go examples.
This change does not affect functionality, only fixes a broken documentation link.
No code changes were made.

Checklist

A couple of things to include in your PR for completeness:

• Updated the typescript README if relevant
• Updated the python README if relevant
• Added a changelog entry
• Added e2e tests if introducing new functionality

[cb-heimdall]

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