The 5.1.x release notes is missing the windows specific information present in the 5.0.x release notes.
"For Windows, .exe installers which were previously deprecated are now removed and replaced with industry-standard MSI installer files. Consequently, any upgrade for the Windows platform from pre-5.0 version to 5.0 will need to be done in a rolling upgrade fashion. See Performing the Rolling Online Upgrade for details."
This part is also missing from the 5.5.x release notes.
The most important part which is also need in all 5.x release notes specifically for windows is
"To upgrade clusters from 4.x to 5.x on Windows, you need to use either the ‘Swap Rebalance’ or the ‘Remove and Rebalance’ method of upgrade. In addition, you must uninstall 4.x and do a fresh installation of 5.x on each node before you add them back into the cluster, since the 5.0 installer is not compatible with pre-existing installations of 4.x and older."