In dr.tex, add a concrete example on a model (by expliciting the matrices)

When doing this, footnote 1 should be updated to reflect that dr1.m has been replaced by stochastic_solvers.

removed milestone

mentioned in commit JohannesPfeifer/dynare@52a03815

mentioned in commit 35b2a24c

mentioned in commit 6e111403

mentioned in issue #1878 (closed)