Add geos installation to README

[lizgzil]

Running

pip install nuts-finder

errors since geos needs to be installed too.

This worked:

conda install geos
pip install nuts-finder

Thus we should add this download step to the installation documentation.

Full error

Collecting nuts-finder
  Using cached nuts_finder-21.5.5.14-py3-none-any.whl (6.6 kB)
Collecting requests==2.22.0
  Using cached requests-2.22.0-py2.py3-none-any.whl (57 kB)
Collecting geojson==2.5.0
  Using cached geojson-2.5.0-py2.py3-none-any.whl (14 kB)
Collecting Shapely==1.6.2.post1
  Using cached Shapely-1.6.2.post1.tar.gz (221 kB)
    ERROR: Command errored out with exit status 1:
     command: /Users/elizabethgallagher/miniconda3/envs/ds/bin/python -c 'import io, os, sys, setuptools, tokenize; sys.argv[0] = '"'"'/private/var/folders/xc/s255_bsx0l7cbx43t290kjtr0000gn/T/pip-install-vbaktxle/shapely_764f598ced6b47b8a8855872ebc1134d/setup.py'"'"'; __file__='"'"'/private/var/folders/xc/s255_bsx0l7cbx43t290kjtr0000gn/T/pip-install-vbaktxle/shapely_764f598ced6b47b8a8855872ebc1134d/setup.py'"'"';f = getattr(tokenize, '"'"'open'"'"', open)(__file__) if os.path.exists(__file__) else io.StringIO('"'"'from setuptools import setup; setup()'"'"');code = f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' egg_info --egg-base /private/var/folders/xc/s255_bsx0l7cbx43t290kjtr0000gn/T/pip-pip-egg-info-sji3r_nz
         cwd: /private/var/folders/xc/s255_bsx0l7cbx43t290kjtr0000gn/T/pip-install-vbaktxle/shapely_764f598ced6b47b8a8855872ebc1134d/
    Complete output (11 lines):
    Failed `CDLL(/Library/Frameworks/GEOS.framework/Versions/Current/GEOS)`
    Failed `CDLL(/opt/local/lib/libgeos_c.dylib)`
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/private/var/folders/xc/s255_bsx0l7cbx43t290kjtr0000gn/T/pip-install-vbaktxle/shapely_764f598ced6b47b8a8855872ebc1134d/setup.py", line 80, in <module>
        from shapely._buildcfg import geos_version_string, geos_version, \
      File "/private/var/folders/xc/s255_bsx0l7cbx43t290kjtr0000gn/T/pip-install-vbaktxle/shapely_764f598ced6b47b8a8855872ebc1134d/shapely/_buildcfg.py", line 185, in <module>
        lgeos = load_dll('geos_c', fallbacks=alt_paths)
      File "/private/var/folders/xc/s255_bsx0l7cbx43t290kjtr0000gn/T/pip-install-vbaktxle/shapely_764f598ced6b47b8a8855872ebc1134d/shapely/_buildcfg.py", line 159, in load_dll
        raise OSError(
    OSError: Could not find library geos_c or load any of its variants ['/Library/Frameworks/GEOS.framework/Versions/Current/GEOS', '/opt/local/lib/libgeos_c.dylib']
    ----------------------------------------
WARNING: Discarding https://files.pythonhosted.org/packages/60/c4/392aff1cb73f20d3cf4bb01a9eeb3eb5db7a167c094d69beca402b9a5846/Shapely-1.6.2.post1.tar.gz#sha256=07fba518e76b3276558f62a5829bdfa476f790cdef752383ccdc8c66b04b0899 (from https://pypi.org/simple/shapely/). Command errored out with exit status 1: python setup.py egg_info Check the logs for full command output.
Collecting nuts-finder
  Using cached nuts_finder-21.5.5.10-py3-none-any.whl (6.6 kB)
  Using cached nuts_finder-0.1.7-py3-none-any.whl (4.0 kB)
  Using cached nuts_finder-0.1.6-py3-none-any.whl (4.0 kB)
  Using cached nuts_finder-0.1.5.tar.gz (3.8 kB)
  Using cached nuts_finder-0.1.4.tar.gz (3.6 kB)
  Using cached nuts_finder-0.1.3.tar.gz (3.6 kB)
  Using cached nuts_finder-0.1.2.tar.gz (2.9 kB)
ERROR: Cannot install nuts-finder==0.1.2, nuts-finder==0.1.3, nuts-finder==0.1.4, nuts-finder==0.1.5, nuts-finder==0.1.6, nuts-finder==0.1.7, nuts-finder==21.5.5.10 and nuts-finder==21.5.5.14 because these package versions have conflicting dependencies.

The conflict is caused by:
    nuts-finder 21.5.5.14 depends on Shapely==1.6.2.post1
    nuts-finder 21.5.5.10 depends on Shapely==1.6.2.post1
    nuts-finder 0.1.7 depends on Shapely==1.6.2.post1
    nuts-finder 0.1.6 depends on Shapely==1.6.2.post1
    nuts-finder 0.1.5 depends on Shapely==1.6.2.post1
    nuts-finder 0.1.4 depends on Shapely==1.6.2.post1
    nuts-finder 0.1.3 depends on Shapely==1.6.2.post1
    nuts-finder 0.1.2 depends on Shapely==1.6.2.post1

To fix this you could try to:
1. loosen the range of package versions you've specified
2. remove package versions to allow pip attempt to solve the dependency conflict

ERROR: ResolutionImpossible: for help visit https://pip.pypa.io/en/latest/user_guide/#fixing-conflicting-dependencies

Maybe we could change the requirements to a newer shapely version? e.g. Shapely 1.8.1.post1