fix formatting

modules/compiler-warnings.md

@@ -31,11 +31,9 @@
 
 ## :wrench: Use the options
 
-Go through the programs written so far and run the compiler using the `-Wall
--Wextra` options.
-	- What kind of problems have you discovered?  How to fix those?
-		- See e.g. #source whole-array.c example above (where only
-		  `-Wextra` gives some clue)
+Go through the programs written so far and run the compiler using the `-Wall -Wextra` options.
+  - What kind of problems have you discovered?  How to fix those?
+    - See e.g. #source whole-array.c example above (where only `-Wextra` gives some clue)
 
 Explore the compiler documentation for more helpful options.  Over the time you
 will find a set of warning options that will serve you well.