Add a docstring to outline metric reader and view configuration conflicts

[lzchen]

Probably out of scope for this but should we clarify somewhere what happens when the metric reader is configured and view also matches.

Originally posted by @srikanthccv in https://github.com/open-telemetry/opentelemetry-python/pull/2832#discussion_r923971127

[srikanthccv]

I believe we no don't need to add an example for this and instead document the spec behavior if we haven't already.