we need to update README to include zlib dependency. just find out that on a fresh installed Ubuntu.

I'm submitting a ...

• improvement request (usability, performance, tech debt, etc.)

Traffic Control components affected ...

• Traffic Ops

Current behavior:

TO currently makes a DB request per server in the ValidateServerCapabilities() function: https://github.com/apache/trafficcontrol/blob/b99eda51b03505f48d67aadf481d16470455a7f4/traffic_ops/traffic_ops_golang/deliveryservic