Inactive maintainers policy (#7467)

Closes: #7449

MAINTAINERS.md

@@ -12,7 +12,16 @@ At present the active maintainers are (alphabetically):
 * Jelle Zijlstra (@JelleZijlstra)
 
 Former and inactive maintainers include:
+
 * David Fisher (@ddfisher)
 * Łukasz Langa (@ambv)
 * Matthias Kramm (@matthiaskramm)
 * Greg Price (@gnprice)
+
+For security reasons, maintainers who haven't been active for twelve months
+(no PR reviews or merges, no opened PRs, no significant participation in
+issues or on typing-sig) will have their access rights removed. They will
+also be moved to the "inactive maintainers" section here.
+
+Inactive maintainers who want their access rights restored should open
+an issue or mail one of the active maintainers.