Added docs and js example for REST API usage

[gwynjudd]

Fixes #38.

Created documentation example showing usage for the REST API

[jglick]

Good to document, though the example presumes familiarity with what I presume is Node.js.

file-parameters-plugin/src/test/java/io/jenkins/plugins/file_parameters/AbstractFileParameterDefinitionTest.java

Line 84 in f2ebf16

// Like: curl -u $auth -F FILE=@/tmp/f $jenkins/job/myjob/buildWithParameters

gives a more succinct tip which requires no programming knowledge, just ability to use a terminal, so I would suggest starting with that before giving examples using assorted programming languages (or the Powershell equivalent with Invoke-WebRequest).

[jglick]

buildWithParameters, especially with file uploads, seems to strain the definition of https://en.wikipedia.org/wiki/Representational_state_transfer#Architectural_constraints. https://www.jenkins.io/doc/book/using/remote-access-api/ does refer to a REST-like style though actually this refers to the read-only “export” system https://javadoc.jenkins.io/component/stapler/org/kohsuke/stapler/export/package-summary.html + https://javadoc.jenkins.io/hudson/model/Api.html. Nitpicking but maybe the wording can be relaxed to just say a “remote” or “HTTP” API?

[gwynjudd]

I can certainly do that. Although since Jenkins itself seems to refer to buildWithParameters as part of their REST API, it will probably be a good idea to at least have that name in a parenthetical note to help people to land in a successful conclusion

[jglick]

Looks good! Left some minor suggestions.