Fix confluent-kafka build error: librdkafka/rdkafka.h file not found
My `pip install confluent-kafka` died compiling because the C headers for librdkafka were missing. Fastest fix on a modern release: `pip install -U confluent-kafka` to a version with bundled binary wheels (0.11.4+), which never compiles anything. If you must build from source, install librdkafka fir…