Add descriptions for types of permissions

Editor assessment

The subject states a concrete documentation addition: descriptions were added for the types of permissions. The docs type fits, no scope is needed, and the change is self-explanatory enough that the missing body is justifiable, since listing permission-type descriptions requires no motivational argument. No footers appear, and nothing is vague: a reader knows which document area grew and why it helps (clarity for permission consumers). Hygiene is clean, with imperative phrasing and no trailing period. A small, complete message that communicates its full intent in one line.