[doc] Add -maxuploadtarget release notes

doc/release-notes.md

@@ -168,6 +168,25 @@ a connection to Tor can be made. It can be configured with the `-listenonion`,
 `-torcontrol` and `-torpassword` settings. To show verbose debugging
 information, pass `-debug=tor`.
 
+Reduce upload traffic
+---------------------
+
+A major part of the outbound traffic is caused by serving historic blocks to
+other nodes in initial block download state.
+
+It is now possible to reduce the total upload traffic via the `-maxuploadtarget`
+parameter. This is *not* a hard limit but a threshold to minimize the outbound
+traffic. When the limit is about to be reached, the uploaded data is cut by not
+serving historic blocks (blocks older than one week).
+Moreover, any SPV peer is disconnected when they request a filtered block.
+
+This option can be specified in MiB per day and is turned off by default
+(`-maxuploadtarget=0`).
+The recommended minimum is 144 * MAX_BLOCK_SIZE (currently 144MB) per day.
+
+A more detailed documentation about keeping traffic low can be found in
+[/doc/reducetraffic.md](/doc/reducetraffic.md).
+
 0.12.0 Change log
 =================