Edit changelog and add 2.6.0-RC1 release notes.

Author: jxblum

spring-session-data-geode/src/main/resources/changelog.txt

@@ -4,6 +4,23 @@ https://github.com/spring-projects/spring-session-data-geode
 ============================================================
 
 
+Changes in version 2.6.0-RC1 (2021-10-20)
+-----------------------------------------
+Aligns Spring Session for Apache Geode (SSDG) with Spring Session (core) 2.6.0-RC1.
+
+* Upgrades to Apache Geode 1.14.0.
+* Upgrades to AssertJ 3.21.0.
+* upgrades to Mockito 4.0.0.
+* Upgrades to SLF4J 1.7.32.
+* Upgrades to Spring Framework 5.3.11.
+* Upgrades to Spring Boot 2.6.0-M3.
+* Upgrades to Spring Data BOM 2021.1.0 (Q-RC1).
+* Upgrades to Spring Data Commons 2.6.0-RC1.
+* Upgrades to Spring Data for Apache Geode 2.6.0-RC1.
+* Upgrades to Spring Security 5.6.0-RC1.
+* Upgrades to Spring Session 2.6.0-RC1.
+
+
 Changes in version 2.5.5 (2021-10-20)
 -------------------------------------
 Aligns Spring Session for Apache Geode (SSDG) with Spring Session (core) 2.5.3.