Update solvers.md

Author: ChrisRackauckas

docs/src/solvers/solvers.md

@@ -63,7 +63,15 @@ customized per-package, details given below describe a subset of important array
     system. 
 - `GenericFactorization(fact_alg)`: Constructs a linear solver from a generic
   factorization algorithm `fact_alg` which complies with the Base.LinearAlgebra
-  factorization API.
+  factorization API. Quoting from Base:
+    - If `A` is upper or lower triangular (or diagonal), no factorization of `A` is
+      required and the system is solved with either forward or backward substitution.
+      For non-triangular square matrices, an LU factorization is used.
+      For rectangular `A` the result is the minimum-norm least squares solution computed by a
+      pivoted QR factorization of `A` and a rank estimate of `A` based on the R factor.
+      When `A` is sparse, a similar polyalgorithm is used. For indefinite matrices, the `LDLt`
+      factorization does not use pivoting during the numerical factorization and therefore the
+      procedure can fail even for invertible matrices.
 
 ### SuiteSparse.jl