Update src/Matrix.jl

Co-authored-by: Max Horn <max@quendi.de>

src/Matrix.jl

@@ -3559,7 +3559,10 @@ i.e. $AB$ is the $n\times n$ unit matrix. If `side` is `:left` and `flag` is
 true, $B$ is the left inverse of $A$ i.e. $BA$ is the $m\times m$ unit matrix.
 If `flag` is false, no right or left inverse exists.
 
-To get the space of all inverses, combine with [`nullspace`](@ref).
+To get the space of all inverses, note that if $B$ and $C$ are
+both right inverses, then $A(B-C)=0$, and similar for left inverses.
+Hence from one inverse one can find all by making suitable use of
+[`nullspace`](@ref).
 """
 function is_invertible_with_inverse(A::MatrixElem{T}; side::Symbol = :left) where {T <: RingElement}
    if (side == :left && nrows(A) < ncols(A)) || (side == :right && ncols(A) < nrows(A))