CodingGuidelines: document formatting of similar config variables.

Document that related `git config` variables should be placed
one-per-line instead of separated by commas.

Suggested-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Collin Funk <collin.funk1@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/CodingGuidelines

@@ -874,6 +874,17 @@ Markup:
 As a side effect, backquoted placeholders are correctly typeset, but
 this style is not recommended.
 
+ When documenting multiple related `git config` variables, place them on
+ a separate line instead of separating them by commas.  For example, do
+ not write this:
+   `core.var1`, `core.var2`::
+	Description common to `core.var1` and `core.var2`.
+
+Instead write this:
+   `core.var1`::
+   `core.var2`::
+	Description common to `core.var1` and `core.var2`.
+
 Synopsis Syntax
 
  The synopsis (a paragraph with [synopsis] attribute) is automatically