Document MALLOC_ARENA_MAX as workaround for glibc memory leak

My task will do a savepoint every hour, so every hour will do a savepoint. From the memory monitoring, it can be seen that the memory of each hour will soar up, although the memory will drop a little later, but from every hour From the point of view of the memory peak on the whole point, the memory continues to rise little by little, and eventually rises to the limited memory, which will lead to being killed by k8S