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- [x] Add new / update outdated documentation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: pydoc_data
  version: 1.0.0 # Nonsense
  tag:
    - always
  top-level:
    - pydoc_data
build:
  type: cpython_module
  script: |
    mkdir dist
    export DISTDIR=$(pwd)/dist
    cd $CPYTHONBUILD/Lib

    tar --exclude=__pycache__ -cf - pydoc_data | tar -C $DISTDIR -xf -

package:
  name: pydoc_data
  version: 1.0.0 # Nonsense
  tag:
    - always
  top-level:
    - pydoc_data
build:
  type: cpython_module
  script: |
    cd $CPYTHONBUILD/Lib

    tar --exclude=__pycache__ -cf - pydoc_data | tar -C $DISTDIR -xf -
