Document use of / in LinearAlgebra (#43632)

Co-authored-by: Viral B. Shah <ViralBShah@users.noreply.github.com>
Co-authored-by: Simon Byrne <simonbyrne@gmail.com>

stdlib/LinearAlgebra/docs/src/index.md

@@ -315,6 +315,7 @@ Other sparse solvers are available as Julia packages.
 ```@docs
 Base.:*(::AbstractMatrix, ::AbstractMatrix)
 Base.:\(::AbstractMatrix, ::AbstractVecOrMat)
+Base.:/(::AbstractVecOrMat, ::AbstractVecOrMat)
 LinearAlgebra.SingularException
 LinearAlgebra.PosDefException
 LinearAlgebra.ZeroPivotException

stdlib/LinearAlgebra/src/generic.jl

@@ -1112,6 +1112,30 @@ function (\)(A::AbstractMatrix, B::AbstractVecOrMat)
 end
 
 (\)(a::AbstractVector, b::AbstractArray) = pinv(a) * b
+"""
+    A / B
+
+Matrix right-division: `A / B` is equivalent to `(B' \\ A')'` where [`\\`](@ref) is the left-division operator.
+For square matrices, the result `X` is such that `A == X*B`.
+
+See also: [`rdiv!`](@ref).
+
+# Examples
+```jldoctest
+julia> A = Float64[1 4 5; 3 9 2]; B = Float64[1 4 2; 3 4 2; 8 7 1];
+
+julia> X = A / B
+2×3 Matrix{Float64}:
+ -0.65   3.75  -1.2
+  3.25  -2.75   1.0
+
+julia> isapprox(A, X*B)
+true
+
+julia> isapprox(X, A*pinv(B))
+true
+```
+"""
 function (/)(A::AbstractVecOrMat, B::AbstractVecOrMat)
     size(A,2) != size(B,2) && throw(DimensionMismatch("Both inputs should have the same number of columns"))
     return copy(adjoint(adjoint(B) \ adjoint(A)))