contributing: Add astyle call for C

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/contributing.md b/contributing.md
index 674dcee..5d64b32 100644
--- a/contributing.md
+++ b/contributing.md
@@ -67,6 +67,9 @@
 
   - Opening braces on the end of a line, except for functions
 
+This style can mostly be verified with 'astyle' as follows:
+
+    astyle --style=linux --indent=tab=8 --indent=force-tab=8
 
 Submitting changes
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