docs(stark-build): docs for base url and deploy url customization support

[christophercr]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/NationalBankBelgium/stark/blob/master/CONTRIBUTING.md#-commit-message-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[X] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: #148

What is the new behavior?

Docs describing the new feature.

Does this PR introduce a breaking change?

[ ] Yes
[X] No

[christophercr]

@dsebastien, @SuperITMan could you have a look on the doc I added and tell me what you think?

[coveralls]

Coverage increased (+0.01%) to 93.785% when pulling bb29f0e on christophercr:feature/basehref-docs into 39d1b43 on NationalBankBelgium:master.