doc: Updates for glossary terms.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Correction and index tags.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Updated with glossary terms.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Updated with glossary terms.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>