Document dependency installation issues related to Kerberos

[wooldridge]

Make it clear in the documentation that the kerberos library dependency can be problematic during the npm install step, particularly on Windows. This is explained some here:

https://www.npmjs.com/package/kerberos

@MayankBhatnagar89 discovered issues during npm install with the kerberos library and Windows 9. This was solved by making sure the following were installed:

• Python 2.7
• Microsoft Visual Studio Express 2013

Previously, @ayuwono solved similar issues by installing:

• x86_64 devel package for glibc

Note: The kerberos library is listed as an optional dependency in package.json. This means users who don't need Kerberos authentication support (the vast majority should not) can skip installation of the kerberos library by running:

npm install --no-optional 

[wooldridge]

@MayankBhatnagar89 mentioned this as being helpful in investigating the issue:

https://gist.github.com/saper/124a63c38bffb0a38d9b

[wooldridge]

Possibly relevant:

https://bugtrack.marklogic.com/42805

[wooldridge]

Updated KERBEROS.md with info on how to skip Kerberos installation for users who do not need it. Windows issues are documented adequately on the kerberos module page, which we link to directly.