Documention of key generation strategy

[tristanlins]

Documentation for #185

[tristanlins]

I had some problems regenerating the site.

First try with regenerate, but the task seems to not be correctly configured:

$ ./node_modules/.bin/gulp regenerate
[10:08:06] Using gulpfile ~/.../spring-data-mock_gh-pages/gulpfile.js
[10:08:06] Starting 'regenerate'...
[10:08:06] Starting 'clean'...
[10:08:06] The following tasks did not complete: regenerate, clean
[10:08:06] Did you forget to signal async completion?

The generate works (after bower install), but there where too much undesired changes: