Update README.md

Signed-off-by: Spencer Bryngelson <[email protected]>

Author: sbryngelson

examples/1D_shuosher/README.md

@@ -1,6 +1,6 @@
 # Shu-Osher problem (1D)
 
-Reference: https://arxiv.org/pdf/2110.05461.pdf.
+Reference: C. W. Shu, S. Osher, Efficient implementation of essentially non-oscillatory shock-capturing schemes, Journal of Computational Physics 77 (2) (1988) 439–471. doi:10.1016/0021-9991(88)90177-5.
 
 ## Initial Condition