Add fixes to support CMake 3.16

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.15)
+cmake_minimum_required(VERSION 3.16)
 project(ScipPP LANGUAGES CXX)
 set(CMAKE_CXX_STANDARD 17)
 
@@ -38,6 +38,7 @@ target_include_directories(ScipPP PUBLIC include)
 target_link_libraries(ScipPP PUBLIC scip::scip)
 
 # install
+include(GNUInstallDirs)
 install(TARGETS ScipPP LIBRARY DESTINATION lib)
 set_target_properties(ScipPP PROPERTIES PUBLIC_HEADER "${SCIPPP_HDR}")
 install(TARGETS ScipPP PUBLIC_HEADER DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/scippp)

readme.md

@@ -145,6 +145,8 @@ the tests) work(s), any kind of dependency management system can be used.
 
 ### Build & Install
 
+Assuming you are using Conan v2 and a CMake version that supports presets (v3.19 and above), run:
+
 ```bash
 conan install -of . .
 cmake --preset conan-release .
@@ -171,6 +173,15 @@ change the install-command to
 conan install -of . --build=missing .
 ```
 
+### If you are using a CMake version without support for presets
+
+```bash
+conan install -of . .
+cmake . -G "Unix Makefiles" -DCMAKE_TOOLCHAIN_FILE=./build/Release/generators/conan_toolchain.cmake -DCMAKE_POLICY_DEFAULT_CMP0091=NEW -DCMAKE_BUILD_TYPE=Release
+make ScipPP
+make install
+```
+
 ### Test
 
 ```bash