MyFirstContribution: clarify asciidoc dependency

Per IRC:

[19:52] <lkmandy> With respect to the MyFirstContribution tutorial, I
will like to suggest this - Under the section "Adding Documentation",
just before the "make all doc" command, it will be really helpful to
prompt a user to check if they have the asciidoc package installed, if
they don't, the command should be provided or they can just be pointed
to install it

So, let's move the note about the dependency to before the build command
blockquote.

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

Author: nasamuffin

Documentation/MyFirstContribution.txt

@@ -507,6 +507,9 @@ documentation is consistent with other Git and UNIX manpages; this makes life
 easier for your user, who can skip to the section they know contains the
 information they need.
 
+NOTE: Before trying to build the docs, make sure you have the package `asciidoc`
+installed.
+
 Now that you've written your manpage, you'll need to build it explicitly. We
 convert your AsciiDoc to troff which is man-readable like so:
 
@@ -522,8 +525,6 @@ $ make -C Documentation/ git-psuh.1
 $ man Documentation/git-psuh.1
 ----
 
-NOTE: You may need to install the package `asciidoc` to get this to work.
-
 While this isn't as satisfying as running through `git help`, you can at least
 check that your help page looks right.