Documentation/CodingGuidelines: spell out more shell guidelines

In earlier days, "imitate the style in the neibouring code" was
sufficient to keep the coherent style, but over time some parts of
the codebase have drifted enough to make it ineffective.

Spell some of the guidelines out.
Signed-off-by: NHeiko Voigt <hvoigt@hvoigt.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/CodingGuidelines

@@ -76,11 +76,19 @@ For shell scripts specifically (not exhaustive):
 
  - We do not use Process Substitution <(list) or >(list).
 
+ - Do not write control structures on a single line with semicolon.
+   "then" should be on the next line for if statements, and "do"
+   should be on the next line for "while" and "for".
+
  - We prefer "test" over "[ ... ]".
 
  - We do not write the noiseword "function" in front of shell
    functions.
 
+ - We prefer a space between the function name and the parentheses. The
+   opening "{" should also be on the same line.
+   E.g.: my_function () {
+
  - As to use of grep, stick to a subset of BRE (namely, no \{m,n\},
    [::], [==], nor [..]) for portability.