[Doc] Update the site2/README.md file (#4130)
[Doc] Update the site2/README.md file (#4130)

### 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.
merlimat/pulsar,merlimat/pulsar,massakam/pulsar,merlimat/pulsar,massakam/pulsar,yahoo/pulsar,massakam/pulsar,yahoo/pulsar,yahoo/pulsar,yahoo/pulsar,massakam/pulsar,yahoo/pulsar,massakam/pulsar,merlimat/pulsar,massakam/pulsar,merlimat/pulsar,yahoo/pulsar,merlimat/pulsar