Add comments.

src/search/cmake/FindCplex.cmake

@@ -13,8 +13,13 @@ set(IMPORTED_CONFIGURATIONS "Debug" "Release")
 set(HINT_PATHS ${cplex_DIR} $ENV{cplex_DIR})
 
 if(WIN32)
+    # On Windows we have to declare the library as SHARED to correctly
+    # communicate the location of the dll and impllib files.
     add_library(cplex::cplex IMPORTED SHARED)
 else()
+    # On Linux, the CPLEX installer sometimes does not provide dynamic
+    # libraries. If they are absent, we fall back to static ones further down,
+    # hence we mark the type unknown here.
     add_library(cplex::cplex IMPORTED UNKNOWN)
 endif()
 set_target_properties(cplex::cplex PROPERTIES