Solution/update docs: node-gyp dependency on Python 2.x

[lfurzewaddock]

The node module 'farmhash' requires node-gyp, which requires python 2.x

Only python 3.x is included in some current LTS distributions (eg. Ubuntu Server 16.04.2 LTS)

Check your environment...

$ python3 -V

...should return the version included in the distribution eg...

Python 3.5.2

However if...

$ python -V

...returns anything other than a version number such as;

The program 'python' can be found in the following packages:

• python-minimal
• python3
  Try: sudo apt install

...then...

$ sudo apt-get update
$ sudo apt-get install python

Check your environment again...

$ python -V

...should return...

Python 2.7.12

The steps above will avoid the following error during npm install;

$ sudo npm install

...generates the following error if python is not available;

farmhash@1.2.1 install /home/lfw/projects/dev/senecajs/ramanujan/node_modules/farmhash
node-gyp rebuild

gyp ERR! configure error
gyp ERR! stack Error: Can't find Python executable "python", you can set the PYTHON env variable.
gyp ERR! stack at failNoPython (/usr/lib/node_modules/npm/node_modules/node-gyp/lib/configure.js:449:14)
gyp ERR! stack at /usr/lib/node_modules/npm/node_modules/node-gyp/lib/configure.js:353:11
gyp ERR! stack at F (/usr/lib/node_modules/npm/node_modules/which/which.js:69:16)
gyp ERR! stack at E (/usr/lib/node_modules/npm/node_modules/which/which.js:81:29)
gyp ERR! stack at /usr/lib/node_modules/npm/node_modules/which/which.js:90:16
gyp ERR! stack at /usr/lib/node_modules/npm/node_modules/which/node_modules/isexe/index.js:44:5
gyp ERR! stack at /usr/lib/node_modules/npm/node_modules/which/node_modules/isexe/access.js:8:5
gyp ERR! stack at FSReqWrap.oncomplete (fs.js:123:15)
gyp ERR! System Linux 4.4.0-77-generic
gyp ERR! command "/usr/bin/nodejs" "/usr/lib/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js" "rebuild"
gyp ERR! cwd /home/lfw/projects/dev/senecajs/ramanujan/node_modules/farmhash
gyp ERR! node -v v6.10.3
gyp ERR! node-gyp -v v3.4.0
gyp ERR! not ok
ramanujan@0.0.1 /home/lfw/projects/dev/senecajs/ramanujan
└── (empty)

npm ERR! Linux 4.4.0-77-generic
npm ERR! argv "/usr/bin/nodejs" "/usr/bin/npm" "install"
npm ERR! node v6.10.3
npm ERR! npm v3.10.10
npm ERR! code ELIFECYCLE

npm ERR! farmhash@1.2.1 install: node-gyp rebuild
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the farmhash@1.2.1 install script 'node-gyp rebuild'.
npm ERR! Make sure you have the latest version of node.js and npm installed.
npm ERR! If you do, this is most likely a problem with the farmhash package,
npm ERR! not with npm itself.
npm ERR! Tell the author that this fails on your system:
npm ERR! node-gyp rebuild
npm ERR! You can get information on how to open an issue for this project with:
npm ERR! npm bugs farmhash
npm ERR! Or if that isn't available, you can get their info via:
npm ERR! npm owner ls farmhash
npm ERR! There is likely additional logging output above.

npm ERR! Please include the following file with any support request:
npm ERR! /home/lfw/projects/dev/senecajs/ramanujan/npm-debug.log
npm ERR! code 1

[leognmotta]

Thank you.