BLD Add DISTDIR variable. ### Description

Adds `DISTDIR` env variable that points to the directory where libraries should be copied to when building shared libraries with recipe.

### Checklists

- [x] Add new / update outdated documentation

package:
  name: distutils
  version: "0.1"
source:
  path: src
test:
  imports:
    - distutils

package:
  name: distutils
  version: "0.1"
source:
  path: src
test:
  imports:
    - distutils
