Update release notes

doc/release/v3_0_0.md

@@ -108,6 +108,11 @@ Important Changes
   Note that `RateThread` used the period in msec(int), `PeriodicThread`
   requires the period in sec(double), so remember to consider a x1000 factor
   when migrate the code.
+* Several methods in public interfaces have a slightly different signature (see
+  #1738 for details).
+* It is now possible to write a `const Portable` on a `Port`.
+* `const Bytes` and `const ManagedBytes` can no longer return non-const pointers
+  to the underlying data.
 
 #### `YARP_dev`
 
@@ -182,6 +187,8 @@ Important Changes
   `IPositionDirect::setPositions(const int, const int*, const double*)`(#1351).
 * The file `yarp/dev/ControlBoardInterfacesImpl.inl` was renamed
   `yarp/dev/ControlBoardInterfacesImpl-inl.h`
+* Several methods in public interfaces have a slightly different signature (see
+  #1738 for details).
 
 #### `YARP_sig`