clarify literate script syntax

The syntax for literate scripts needs to be clarified. See the thread http://www.haskell.org/pipermail/haskell-cafe/2007-March/023027.html for more details.

The report should also give a reference unlitter. I'll attach (an untested) one from the above thread.

Trac metadata

Trac field	Value
Version
Type	Task
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	HaskellPrime
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed weight to 5

added Trac import task labels

assigned to @trac-none and unassigned @trac-ijones

Trac metadata

Trac field	Value
Component	HaskellPrime → Proposal

changed milestone to %⊥

moving non-milestoned many year old legacy tickets out of the way

Set default priority (as this confuses Trac otherwise)