Update Other Resources episode with Instructor note, additional resources

[bencomp]

The episode "Other Resources in OpenRefine" has two similar sections about learning more about OpenRefine using (un)official help resources, and one discussion exercise. The objectives of the episode are to know about and find further resources to continue learning.

The text is a bit vague, in my opinion. Phrases like "a lot more", "great introductory videos", "a lot of help" do not explain why you may want to use the additional resources, or what there is to learn beyond what was covered in the lesson.

Some of the suggested resources are linked directly, others (like videos) are left to readers to find. I think it would be good to elaborate a little on what the other resources can teach learners/readers and to provide (more) direct links to the resources.

As suggested in #122 (comment), an Instructor note could be added to explain that not all resources need to be discussed.