message: Update readme for 2.6.0
diff: @@ -217,6 +217,9 @@ Feel free to send PRs on any of these issues.
  ## Release Change Log
  +* 2.6.0
  + - Merged [PR#79](https://github.com/XeroAPI/xero-node/pull/79) - Add support for ContactGroups
  + - Merged [PR#80](https://github.com/XeroAPI/xero-node/pull/80) - Fixes Contact address deatil schema.
  * 2.5.3
  - Merged [PR#76](https://github.com/XeroAPI/xero-node/pull/76) - Updated the docs to add repeating invoices (missed from PR#72).
  - Merged [PR#75](https://github.com/XeroAPI/xero-node/pull/75) - Added documentation about invoice/contact filters.
  