doc(linear_algebra/basic): add module and declaration doc strings (#1501)
doc(linear_algebra/basic): add module and declaration doc strings (#1501)

* doc(linear_algebra/basic): declaration doc strings

* doc(linear_algebra/basic): improve module doc

* Update src/linear_algebra/basic.lean

Co-Authored-By: Floris van Doorn <04eee3258902297ef5081ba8b0786f6ab1274795@gmail.com>

leanprover-community/mathlib,leanprover-community/mathlib