DOC: mention William as maintainer of the cache and master-worker

The latter is very tricky, better not touch anything there without
his approval.
diff --git a/MAINTAINERS b/MAINTAINERS
index ea0060a..35c1043 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -61,3 +61,11 @@
 51Degrees device identification
 Maintainer: Ben Shillito <ben@51degrees.com>
 Files: src/51d.c
+
+Cache
+Maintainer: William Lallemand <wlallemand@haproxy.com>
+Files: src/cache.c, include/*/cache.h
+
+Master-worker
+Maintainer: William Lallemand <wlallemand@haproxy.com>
+Note: Please CC William when touching src/haproxy.c and contrib/systemd