Add 5.0 to info file for clarity

Created by: eileenmcnaughton

Info about versions dev/release#1 (comment 2843)

In the 4.x series, tags mean the same as today. (Exact-match to version. An extension declaring <ver>4.6</ver> is not displayed for download on 4.7.) In the 5.x series, <ver> tags imply forward compatibility. (An extension declaring <ver>5.2</ver> is displayed on 5.2, 5.3, etc. But not on 5.0.) To bridge them, 4.7 is forward compatible with 5.0. (An extension declaring <ver>4.7</ver> is displayed on 4.7, 5.0, 5.1, etc.) As today, a consumer sees the newest extensions that are compatible with their version.