The install path for the README and LICENSE files is hardcoded to
"/usr/share/doc/tenacity", change this to use the INSTALL_DOCDIR
defined by cmake.eclass

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 61e61f597..4359bccf7 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -1393,7 +1393,7 @@ else()
       install( FILES "${_INTDIR}/${APP_NAME}.desktop"
                DESTINATION "${_DATADIR}/applications" )
       install( FILES "${CMAKE_SOURCE_DIR}/LICENSE.txt" "${CMAKE_SOURCE_DIR}/README.md"
-               DESTINATION "${_DATADIR}/doc/${APP_NAME}" )
+               DESTINATION "${CMAKE_INSTALL_DOCDIR}" )
       install( FILES "${_SRCDIR}/tenacity.xml"
                DESTINATION "${_DATADIR}/mime/packages" )
       install( FILES "${CMAKE_SOURCE_DIR}/presets/EQDefaultCurves.xml"