Docs: describe how/what can be injected

[d-koppenhagen]

Describe

  app.provide("ol-options", options);
  app.provide("ol-feature", feature);
  app.provide("ol-geom", geom);
  app.provide("ol-animations", animations);
  app.provide("ol-format", format);
  app.provide("ol-loadingstrategy", loadingstrategy);
  app.provide("ol-selectconditions", selectconditions);
  app.provide("ol-extent", extent);