ENH: Added documentation of VERSION and SOVERSION properties.

Source/cmSetTargetPropertiesCommand.h

@@ -65,6 +65,12 @@ public:
         "sources.  PRE_INSTALL_SCRIPT specifies CMake script that is run "
         "prior to installing the target. POST_INSTALL_SCRIPT specifies "
         "CMake script that is run after target is installed. "
+        "For shared libraries VERSION and SOVERSION can be used to specify "
+        "the build version and api version respecitvely. When building or "
+        "installing appropriate symlinks are created if the platform "
+        "supports symlinks and the linker supports so-names. "
+        "If only one of both is specified the missing is assumed to have "
+        "the same version number. "
         "The OUTPUT_NAME can be used to set an output name that is "
         "used in place of the target name when creating executables."
         "If not set here then it is set to target_EXPORTS by default "