added example to readme

README.md

@@ -22,4 +22,11 @@ This is a basic example which shows you how to solve a common problem:
 
 ``` r
 library(gmresls)
+# prepare a 4x3 toy problem Ax=b
+A=rbind(diag(1:3)+matrix(1, 3,3), rep(1, 3))
+xsol=1:3
+b=A%*%xsol
+f_Ax=function(x,...) list(...)$A%*%x
+f_Br=function(r,...) t(list(...)$A)%*%r
+x=gmresls(f_Ax, f_Br, b, A=A)
 ```