Fix some typos in the building native image documentation

[sturdy5]

As I'm learning how to work through some of the quarkus stuff I've found a couple typos in the documentation. The two changes in this request are straightforward.

1. Fix grammar in referencing application endpoints
2. The section that talks about building a container using the native-micro Dockerfile wasn't using the same file in the examples

[gsmet]

Thanks for taking the time to create a pull request!