CONTRIBUTING.md: Add JavaScript .clang-format file

Added a new JavaScript section to the "Coding style" section.

Change-Id: Ic992efa98500c421504da602fbc96f18e608a074
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 0ec880d..f59fe9f 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -83,6 +83,16 @@
 ignore= NONE
 ```
 
+### JavaScript
+
+A .clang-format file that closely approximates our JavaScript coding style is:
+```
+---
+Language:        JavaScript
+BasedOnStyle:    Google
+ColumnLimit:     80
+```
+
 ### C
 
 For C code, we typically use the Linux coding style, which is documented at: