Added CHANGELOG and version description

CHANGELOG.md

@@ -0,0 +1,41 @@
+Changelog
+=========
+
+__v2.4__
+--------
+
+*   Stability improvements
+*   Support for secondary instances.
+*   The library now recovers safely after the primary process has crashed
+    and the shared memory had not been deleted.
+
+__v2.3__
+--------
+
+*   Improved pimpl design and inheritance safety.
+
+    _Vladislav Pyatnichenko_
+
+__v2.2__
+--------
+
+*   The `QAPPLICATION_CLASS` macro can now be defined in the file including the
+Single Application header or with a `DEFINES+=` statement in the project file.
+
+__v2.1__
+--------
+
+*   A race condition can no longer occur when starting two processes nearly
+    simultaneously.
+
+    Fix issue [#3](https://github.com/itay-grudev/SingleApplication/issues/3)
+
+__v2.0__
+--------
+
+*   SingleApplication is now being passed a reference to `argc` instead of a
+    copy.
+
+    Fix issue [#1](https://github.com/itay-grudev/SingleApplication/issues/1)
+
+*   Improved documentation.

README.md

@@ -106,6 +106,15 @@ will replace it as Primary even if the `--secondary` argument has been set.
 *P.S. If you think this behavior could be improved create an issue and explain
 why.*
 
+Versioning
+----------
+
+The current library versions is `2.4`.
+Each major version introduces either very significant changes or is not
+backwards compatible with the previous version. Minor versions only add
+additional features, bug fixes or performance improvements and are backwards
+compatible with the previous release.
+
 Implementation
 --------------