Added RAT Tutorial & Bug Fixed (#92) in Routing Code & download link updated

[SanchitMinocha]

Added RAT Tutorial for beginners on 2019 Karnataka Floods.

Fixed Bug in Routing Code where it used to fail for end date in the month of February of a leap year. To address #92, we have updated Routing code as follows:

c     calculate number of days & months in simulation
      M=START_MO
      Y=START_YEAR
      NMONTHS = 0
      NDAY=0
      DO J=START_MO,12*(STOP_YEAR-START_YEAR)+STOP_MO
        IF(M.EQ.2) THEN
           LP=isaleap(Y)
        ELSE 
           LP=0
        ENDIF
        NDAY = NDAY+DAYS_IN_MONTH(M)+LP
        NMONTHS = NMONTHS + 1
        MO(NMONTHS) = M
        YR(NMONTHS) = Y
        M = M + 1
        IF (M .GT. 12) THEN
            M = 1
            Y  = Y + 1
        ENDIF
      END DO
      IF(NDAY.GT.DAYS) THEN
         PRINT*, 'IN ROUT.F RESET DAYS TO ', NDAY
         STOP
      ENDIF
      IF(STOP_MO.EQ.2) THEN
         LP=isaleap(STOP_YEAR)
      ELSE 
         LP=0
      ENDIF
	  NDAY = NDAY-(START_DAY-1)-(DAYS_IN_MONTH(STOP_MO)+LP-STOP_DAY)
      PRINT*,'NDAY = ',NDAY, ' NMONTHS = ',NMONTHS

The code has been changed from seventh last line to second last line.

[pritamd47]

Great tutorial, thanks for adding instructions on how to get started with RAT. The code and added documentation files look good to be merged.