Feat: add CPack support (yhirose#1950)

Author: zjyhjqs

CMakeLists.txt

@@ -299,6 +299,8 @@ if(HTTPLIB_INSTALL)
 	# ex: /usr/share/doc/httplib/README.md and /usr/share/licenses/httplib/LICENSE
 	install(FILES "README.md" DESTINATION "${CMAKE_INSTALL_DOCDIR}")
 	install(FILES "LICENSE" DESTINATION "${CMAKE_INSTALL_DATADIR}/licenses/${PROJECT_NAME}")
+
+	include(CPack)
 endif()
 
 if(HTTPLIB_TEST)