* Add test for links to other markdown docs.

* Remove unused import.

### Motivation
When writing Pulsar docs, we can adopt a consistent writing styles, whoever the author is.
Here I introduce [Google Developer Documentation Style Guide](https://developers.google.com/style/) for Pulsar technical docs. The style guide generally conforms to with most popular technical writing styles, such as *IBM style guides*, *Microsoft style guide*, *The Chicago Manual of Style*, and so on.
In addition, *Google Developer Documentation Style Guide* is open to all, and the link is easy to share among all participants.

### Modifications
1. Restructure the content of the site2/reademe file: website, doc, and translation.
2. Introduce *Google Developer Documentation Style Guide* in **Contribute to documentation**.

* [website] Add instructions on how to download translated docs

* Adopt Jennifer's changes

* Update the README with more instructions

### Motivation
We've applied GSoD project for Pulsar docs, and more contributors might read this file, I some typos when reading the document. 

### Modifications
1. Delete the redundant link and information on versioning for Line 169.
2. Refine some sentences to be a little more smooth.
3. Improve notes in the `Running the site locally` section.

* Clarify version match requirements between Go and C++ client librarires

* Document how to see local changes

* Link to docs README

* Move warning out from `go get` paragraph

* Removed mentions to incubator-pulsar

* Removed DISCLAIMER link from offloaders package

* Trigger build

### Motivation

Improve the documentation and usability of the pulsar website. This moves the website and documentation to a new framework (https://docusaurus.io/)  which will make it easier to maintain going forward.

### Modifications

A new version of the website in site2 directory. Also updates the pulsar build docker to add the new website build dependencies.

### Result

A more usable website and documentation.

A preview of the site can be seen here: https://cckellogg.github.io/incubator-pulsar
*All the links and images might not work on this site since it's a test only site*