Include gettext.h in MyFirstContribution tutorial

The tutorial in Documentation/MyFirstContribution.txt has steps to print
some text using the "_" function. However, this leads to compiler errors
when running "make" since "gettext.h" is not #included.

Update docs with a note to #include "gettext.h" in "builtin/psuh.c".

Signed-off-by: Jacob Stopak <[email protected]>
Reviewed-by: Emily Shaffer <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: initialcommit-io

Documentation/MyFirstContribution.txt

@@ -160,10 +160,11 @@ in order to keep the declarations alphabetically sorted:
 int cmd_psuh(int argc, const char **argv, const char *prefix);
 ----
 
-Be sure to `#include "builtin.h"` in your `psuh.c`.
+Be sure to `#include "builtin.h"` in your `psuh.c`. You'll also need to
+`#include "gettext.h"` to use functions related to printing output text.
 
-Go ahead and add some throwaway printf to that function. This is a decent
-starting point as we can now add build rules and register the command.
+Go ahead and add some throwaway printf to the `cmd_psuh` function. This is a
+decent starting point as we can now add build rules and register the command.
 
 NOTE: Your throwaway text, as well as much of the text you will be adding over
 the course of this tutorial, is user-facing. That means it needs to be