CODING_STYLE: Add notes on avoiding trailing whitespace.

CODING_STYLE

@@ -132,7 +132,7 @@ structure definition:
 
 	struct _cairo_gstate {
 	    cairo_operator_t op;
-    
+
 	    double tolerance;
 
 	    /* stroke style */
@@ -146,19 +146,33 @@ structure definition:
 	    double *dash;
 	    int num_dashes;
 	    double dash_offset;
-	
+
 	    ...
 	}
 
 Use a single space before a left parenthesis, except where the
 standard will not allow it, (eg. when defining a parameterized macro).
 
-Don't eliminate whitespace just because things would still fit on one
+Don't eliminate newlines just because things would still fit on one
 line. This breaks the expected visual structure of the code making it
 much harder to read and understand:
 
 	if (condition) foo (); else bar ();	/* Yuck! */
 
+Do eliminate trailing whitespace (space or tab characters) on any
+line. Also, avoid putting intial or final blank lines into any file,
+and never use multiple blank lines instead of a single blank line.
+
+Do enable the default git pre-commit hook that detect trailing
+whitespace for you and help you to avoid corrupting cairo's tree with
+it. Do that as follows:
+
+	chmod a+x .git/hooks/pre-commit
+
+You might also find the git-stripspace utility helpful which acts as a
+filter to remove trailing whitespace as well as initial, final, and
+duplicate blank lines.
+
 As a special case of the bracing and whitespace guidelines, function
 definitions should always take the following form: