[gjs: 11/12] docs: Add note about building SpiderMonkey

[Philip Chimento <pchimento src gnome org>]

commit c2f07e3977fd6086130910a94e5b59bf59146e42
Author: Philip Chimento <philip chimento gmail com>
Date:   Sat Apr 3 18:12:35 2021 -0700

    docs: Add note about building SpiderMonkey
    
    It's confusing here because you don't need a debug-enabled SpiderMonkey
    unless you're writing C++ code.

 doc/Hacking.md | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
---
diff --git a/doc/Hacking.md b/doc/Hacking.md
index 0983ca14..3c2d3e5b 100644
--- a/doc/Hacking.md
+++ b/doc/Hacking.md
@@ -49,11 +49,15 @@ SpiderMonkey cannot be auto-installed, so you will need to install it
 either through your system's package manager, or building it yourself.
 Even if your system includes a development package for SpiderMonkey, we
 still recommend building it if you are going to do any development on
-GJS so that you can enable the debugging features.
+GJS's C++ code so that you can enable the debugging features.
 These debugging features reduce performance by quite a lot, but they
 will help catch mistakes in the API that could otherwise go unnoticed
 and cause crashes in gnome-shell later on.
 
+If you aren't writing any C++ code, then you don't need to build it
+yourself. Install SpiderMonkey using your system's package manager
+instead.
+
 To build SpiderMonkey, follow the instructions on [this 
page](https://github.com/mozilla-spidermonkey/spidermonkey-embedding-examples/blob/esr78/docs/Building%20SpiderMonkey.md)
 to download the source code and build the library.
 If you are using `-Dprefix` to build GJS into a different path, then
 make sure to use the same build prefix for SpiderMonkey with `--prefix`.