made some clarifications

docs/exercise3.rst

@@ -19,7 +19,9 @@ command line flags. These are:
     - Animate
 
 The corresponding fireworks with test inputs can be found in 
-**exercises/demos/3_files_and_commands**.
+**exercises/demos/3_files_and_commands**. The provided solutions in 
+**exercises/solutions/3_files_and_commands** are suitable for the input for 
+letter "A" in **exercises/inputs/3_files_and_commands/A**. 
 
 Problem 3.1
 -----------
@@ -31,8 +33,8 @@ to recover all tiles and put them together to reconstruct the image of the
 selected letter.
 
 Select input images for a letter from the folder **exercises/inputs/3_files_and_commands**. 
-Then use the provided fireworks adjusting the concrete parameters, inputs and 
-outputs and compose a workflow for the selected letter. Verify, add and run the 
+Then use the provided fireworks and compose a workflow for the selected letter 
+by adjusting the concrete parameters, inputs and outputs. Verify, add and run the 
 workflow and check the resulting image.