Updated to clarify versioning behavior
Updated to clarify versioning behavior

Fixed a few things with version-related documentation: 

* clarified the relationship of typings package version vs. library versions
* explained how package versions and library versions can get out of sync
* fixed broken links in major-version-upgrade section
* clarified major-version-upgrade section

See #25677 for more discussion and background for these changes.
dsebastien/DefinitelyTyped,georgemarshall/DefinitelyTyped,borisyankov/DefinitelyTyped,mcliment/DefinitelyTyped,dsebastien/DefinitelyTyped,georgemarshall/DefinitelyTyped,markogresak/DefinitelyTyped,georgemarshall/DefinitelyTyped,borisyankov/DefinitelyTyped,georgemarshall/DefinitelyTyped