[bazel.build] Problem with /start/cpp

### Page link:

https://bazel.build/start/cpp

### Problem description (include actual vs expected text, if applicable):

The BUILD file on the page doesn't match what's in the GitHub repository for the examples.

This caused me to get errors when I tried to set up my own project and didn't understand that you needed to have `load()` in there. The errors I saw did tell me about `load`, but I wasn't sure why I needed it, when the example on the page didn't include it.

### Where do you see this issue? (include link to specific section of the page, if applicable)

https://bazel.build/start/cpp#understand-build
https://github.com/bazelbuild/examples/blob/main/cpp-tutorial/stage1/main/BUILD

### Any other information you'd like to share?

_No response_

Compare the /start/cpp#understand-build page with the referenced examples/cpp-tutorial/stage1/main/BUILD file, paying particular attention to the missing load() statement. Update the page example and explanation to match the repository example, then verify that the documented setup no longer conflicts with the linked BUILD file.

Written by the indexing model from the issue text.