Init Polish localization (#18419) (#18659)

Initial commit for Polish localization

* Translation style reviewed and improved by:
  Michał Sochoń <kaszpir@gmail.com>
  Karol Pucyński <kpucynski@gmail.com>
  with contribution from Wojciech Kocjan <wojciech@kocjan.org>

* Kubernetes slogan translated by Karol Pucyński
* Corectness of non-language-specific content reviewed and improved by:
  Tim Bannister <tim@scalefactory.com>

content/pl/examples/minikube/Dockerfile

@@ -0,0 +1,4 @@
+FROM node:6.14.2
+EXPOSE 8080
+COPY server.js .
+CMD node server.js

content/pl/examples/minikube/server.js

@@ -0,0 +1,9 @@
+var http = require('http');
+
+var handleRequest = function(request, response) {
+  console.log('Received request for URL: ' + request.url);
+  response.writeHead(200);
+  response.end('Hello World!');
+};
+var www = http.createServer(handleRequest);
+www.listen(8080);