docs: update release information for v2.6

Updated tentative code freeze and release target date for v2.6
release.

Change-Id: I3dd6cfef1a07f3e0159ec7996d18f6cbcb975da7
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>

docs/about/release-information.rst

@@ -46,6 +46,8 @@ depending on project requirement and partner feedback.
 +-----------------+---------------------------+------------------------------+
 | v2.5            | 3rd week of May '21       | 5th week of Apr '21          |
 +-----------------+---------------------------+------------------------------+
+| v2.6            | 4th week of Oct '21       | 1st week of Oct '21          |
++-----------------+---------------------------+------------------------------+
 
 Removal of Deprecated Interfaces
 --------------------------------