Simple Alert on High Memory Load

[xluffy]

I don't understand why must calculator a complex expression for triggering a high load memory alert. node_exporter is supported node_memory_MemAvailable for checking available memory. Just use

IF (node_memory_MemTotal - node_memory_MemAvailable) / node_memory_MemTotal * 100 > 85

Any reason to use old expression?

[saied-nawaz]

Hi @xluffy thanks for the suggestion. Do you want to open a PR with the changes