Update references (#319)

Author: mschauer

docs/src/linear_systems/idrs.md

@@ -11,7 +11,11 @@ idrs!
 
 ## Implementation details
 
-The current implementation is based on the [MATLAB version](http://ta.twi.tudelft.nl/nw/users/gijzen/idrs.m) by Van Gijzen and Sonneveld. For background see [^Sonneveld2008], [^VanGijzen2011] and [the IDR(s) webpage](http://homepage.tudelft.nl/1w5b5/idrs-software.html).
+The current implementation is based on the [MATLAB version](http://ta.twi.tudelft.nl/nw/users/gijzen/idrs.m) by 
+Van Gijzen and Sonneveld. For background see [^Sonneveld2008], [^VanGijzen2011], [the IDR(s) webpage](http://homepage.tudelft.nl/1w5b5/idrs-software.html)
+and the IDR chapter in [^Meurant2020]. 
 
 [^Sonneveld2008]: IDR(s): a family of simple and fast algorithms for solving large nonsymmetric linear systems. P. Sonneveld and M. B. van Gijzen SIAM J. Sci. Comput. Vol. 31, No. 2, pp. 1035--1062, 2008
-[^VanGijzen2011]: Algorithm 913: An Elegant IDR(s) Variant that Efficiently Exploits Bi-orthogonality Properties. M. B. van Gijzen and P. Sonneveld ACM Trans. Math. Software,, Vol. 38, No. 1, pp. 5:1-5:19, 2011
+[^VanGijzen2011]: Algorithm 913: An Elegant IDR(s) Variant that Efficiently Exploits Bi-orthogonality Properties. M. B. van Gijzen and P. Sonneveld ACM Trans. Math. Software, Vol. 38, No. 1, pp. 5:1-5:19, 2011
+[^Meurant2020]: The IDR family. G. Meurant and J. Duintjer Tebbens. In: Krylov Methods for Nonsymmetric Linear Systems. Springer Series in Computational Mathematics, vol 57. Springer, 2020. [doi:10.1007/978-3-030-55251-0_10](https://doi.org/10.1007/978-3-030-55251-0_10)
+