OsmoGSMTester: document logrotate maxsize

Change-Id: Ib3e7143eb5d90eea4860a0a334da25efe926a231
diff --git a/doc/manuals/chapters/install.adoc b/doc/manuals/chapters/install.adoc
index 4d2b677..6eef2fa 100644
--- a/doc/manuals/chapters/install.adoc
+++ b/doc/manuals/chapters/install.adoc
@@ -484,6 +484,14 @@
 gpasswd -a jenkins usrp
 ----
 
+==== Log Rotation
+
+To avoid clogging up /var/log, it makes sense to choose a sane maximum log size:
+
+----
+echo maxsize 10M > /etc/logrotate.d/maxsize
+----
+
 ==== Install Scripts
 
 IMPORTANT: When using the jenkins build slave as configured above, *there is no