docker build error

Collecting Pillow==6.1.0 (from -r /mnt/extra-addons/requirements.txt (line 42))
  Downloading https://files.pythonhosted.org/packages/d6/98/0d360dbc087933679398d73187a503533ec0547ba4ffd2115365605559cc/Pillow-6.1.0-cp35-cp35m-manylinux1_x86_64.whl (2.1MB)
Collecting polib==1.1.0 (from -r /mnt/extra-addons/requirements.txt (line 43))
  Downloading https://files.pythonhosted.org/packages/30/a2/e407c3b00cace3d7fc8df14d364deeecfeb96044e1a317de583bc26eae58/polib-1.1.0-py2.py3-none-any.whl
Collecting psutil==4.3.1 (from -r /mnt/extra-addons/requirements.txt (line 44))
  Downloading https://files.pythonhosted.org/packages/78/cc/f267a1371f229bf16db6a4e604428c3b032b823b83155bd33cef45e49a53/psutil-4.3.1.tar.gz (315kB)
Collecting psycopg2==2.8.3 (from -r /mnt/extra-addons/requirements.txt (line 45))
  Downloading https://files.pythonhosted.org/packages/5c/1c/6997288da181277a0c29bc39a5f9143ff20b8c99f2a7d059cfb55163e165/psycopg2-2.8.3.tar.gz (377kB)
    Complete output from command python setup.py egg_info:
    running egg_info
    creating pip-egg-info/psycopg2.egg-info
    writing top-level names to pip-egg-info/psycopg2.egg-info/top_level.txt
    writing dependency_links to pip-egg-info/psycopg2.egg-info/dependency_links.txt
    writing pip-egg-info/psycopg2.egg-info/PKG-INFO
    writing manifest file 'pip-egg-info/psycopg2.egg-info/SOURCES.txt'

    Error: pg_config executable not found.

    pg_config is required to build psycopg2 from source.  Please add the directory
    containing pg_config to the $PATH or specify the full executable path with the
    option:

        python setup.py build_ext --pg-config /path/to/pg_config build ...

    or with the pg_config option in 'setup.cfg'.

    If you prefer to avoid building psycopg2 from source, please install the PyPI
    'psycopg2-binary' package instead.

    For further information please check the 'doc/src/install.rst' file (also at
    <http://initd.org/psycopg/docs/install.html>).


    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-build-jujgbri8/psycopg2/
The command '/bin/bash -xo pipefail -c pip3 install --no-cache-dir -r /mnt/extra-addons/requirements.txt' returned a non-zero code: 1