amari.xlog: Clarify why we will need to implement log rotation ourselves

Upon rotation we want to emit trailing part to the old file, and emit
new header into new log file. All this is custom and cannot be handled
reliably when rotation is done by external tool.

amari/xlog.py

@@ -48,6 +48,14 @@
 
 
 # TODO log file + rotate
+#
+# Rejected alternative: automatic rotation by an external tool, e.g. log_proxy:
+#      see https://github.com/metwork-framework/log_proxy
+#      and https://superuser.com/questions/291368/log-rotation-of-stdout
+#
+#      reason for rejection: on every rotation we want to emit "end of file"
+#                            entries to old file + header to new file.
+
 # TODO log loading -> DataFrame