After I added that in, I got this:
C:\Users\xxxx\AppData\Local\Temp\cclEKYDs.ltrans0.ltrans.o: In function `global constructors keyed to 65535_0_sketch_nov24a.ino.cpp.o.4294':
<artificial>:(.text.startup+0x1ce): undefined reference to `DHT::DHT(unsigned char, unsigned char, unsigned char)'
C:\Users\xxxx\AppData\Local\Temp\cclEKYDs.ltrans0.ltrans.o: In function `setup':
D:\Downloads\sketch_nov24a/sketch_nov24a.ino:29: undefined reference to `DHT::begin(unsigned char)'
C:\Users\xxxx\AppData\Local\Temp\cclEKYDs.ltrans0.ltrans.o: In function `loop':
D:\Downloads\sketch_nov24a/sketch_nov24a.ino:74: undefined reference to `DHT::readHumidity(bool)'
collect2.exe: error: ld returned 1 exit status