Describe the issue linked to the documentation

In the user guide for pipelines the demonstration of the construction of a pipeline includes two examples:

1. Directly creating a new instance of Pipeline.
2. Using the utility function make_pipeline.

Each example uses different lists of estimators, whereas it would be clearer if both examples used the same estimators.

Suggest a potential alternative/fix

Both examples should use the same estimators when creating a Pipeline, namely the combination of PCA and SVC as in the first example.

In the file doc/modules/compose.rst lines 68-72 should be replaced with the following
>>> make_pipeline(PCA(), SVC())
Pipeline(steps=[('reduce_dim', PCA()), ('clf', SVC())])