ReadMe add step `go get ...` see provided patch to fix it

### 👓 What did you see?

For someone new to Go and godog the Readme could be improved by providing more hints / steps to do.
See [surfmuggle-patch-1](https://github.com/surfmuggle/godog/tree/surfmuggle-patch-1) to fix it.

### File `go.sum`

- Expected File `go.sum` exists
- Actual `go.sum` does not exists

According to the README these files should be present

As far as i can tell i did every step of the readme. But the file `sum.go` is missing in my folder.


To my understanding `sum.go` is not created yet, because no building command (like `go build`, `go test`) has been run yet.

### Running `go test`

- Expected: `go test` results in `testing: warning: no tests to run PASS ok godogs`
- Actual: `go test` results in a FAIL see below

```bash
C:\dev\golang\src\TestHello\godogs>go test
# godogs
godogs_test.go:3:8: no required module provides package github.com/cucumber/godog; to add it:
go get github.com/cucumber/godog
FAIL godogs [setup failed]
```

### ✅ What did you expect to see?

Add `go get github.com/cucumber/godog` above the phrase `Our module should now look like this:`.
See this [godog-my-patch-1](https://github.com/surfmuggle/godog/tree/surfmuggle-patch-1) to fix it.

### 📦 Which tool/library version are you using?

### 🔬 How could we reproduce it?

Steps to reproduce the behavior:
1. Install '...' version '...'
2. Create a file called '....'
3. Run command '....'
4. See error '....'

### 📚 Any additional context?

----

*This text was originally generated from a [template](https://docs.github.com/en/communities/using-templates-to-encourage-useful-issues-and-pull-requests/about-issue-and-pull-request-templates), then edited by hand. [You can modify the template here.](https://github.com/cucumber/.github/edit/main/.github/ISSUE_TEMPLATE/bug_report.md)*

Start in the README section before “Our module should now look like this:” and compare the documented steps with the provided surfmuggle-patch-1 reference. Run the reported go test setup to confirm the missing dependency guidance, then verify that the README includes go get github.com/cucumber/godog and shows the expected go.sum flow.

Written by the indexing model from the issue text.