Adjust README with comments from the per-release doc review. (#11110)
Adjust README with comments from the per-release doc review. (#11110)

* Adjust README with comments from the per-release doc review.
* Make additional breadcrumb to samples higher in the page, duplication is OKd (and even recommended) in this case.
* Removed spurious FIFO reference.
* Added a note about preview vs. existing docs, with breadcrumb to existing libs.
* Make 0.50 doc links more specific.
Azure/azure-sdk-for-python,Azure/azure-sdk-for-python,Azure/azure-sdk-for-python,Azure/azure-sdk-for-python