Update 04-pipefilter.md to reflect current episode structure

episodes/04-pipefilter.md

@@ -6,16 +6,18 @@ exercises: 10
 
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+- Explain the advantage of linking commands with pipes and filters.
+- Combine sequences of commands to get new output
 - Redirect a command's output to a file.
-- Construct command pipelines with two or more stages.
 - Explain what usually happens if a program or pipeline isn't given any input to process.
-- Explain the advantage of linking commands with pipes and filters.
 
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 :::::::::::::::::::::::::::::::::::::::: questions
 
-- How can I combine existing commands to do new things?
+- How can I combine existing commands to produce a desired output?
+- How can I show only part of the output? 
+- How can I combine existing commands to do new things? ( -> pipes)
 
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