tcp: updated CHANGES.html and RELEASE_NOTES

CHANGES.html

@@ -54,6 +54,9 @@ us a note on ns-developers mailing list.</p>
 <h1>Changes from ns-3.26 to ns-3.27</h1>
 <h2>New API:</h2>
 <ul>
+<li>Included the TCP SACK-based loss recovery algorithm outlined in RFC 6675</li>
+<li>Added <b>TCP SACK</b> and the <b>SACK emulation</b>. Added an Attribute to TcpSocketBase class,
+    called "Sack", to enable or disable the SACK option usage.</li>
 <li>In 'src/wifi', several changes were made to enable partial <b>802.11ax</b> High Effiency (HE) support:
     <ul>
       <li>A new standard value has been added that enables the new 11ax data rates.</li>

RELEASE_NOTES

@@ -22,11 +22,13 @@ Supported platforms
 New user-visible features
 -------------------------
 - (wifi) 802.11ax High Efficiency (HE) physical layer modes are now supported.
+- (tcp) The SACK option and the RFC 6675 loss recovery algorithm are now supported.
 
 Bugs fixed
 ----------
 - Bug 2007 - uan: Remove deprecation on SetRxThresholdDb
 - Bug 2221 - network: Remove constraint on size of ns3::Packet Tag objects
+- Bug 2248 - TCP SACK
 - Bug 2263 - Support processing of multiple TCP options
 - Bug 2450 - LogDistancePropagationLossModel is not continuous
 - Bug 2463 - create trace source to trace the TXOP time that is actually used