[libadwaita/wip/exalm/flatpak-docs] docs: Add sassc to the flatpak manifest example

[Alexander Mikhaylenko <alexm src gnome org>]

commit c9fd053d67bac8bd46d6fbfcb562f9a2d2dfc60b
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Sat Jul 10 00:42:00 2021 +0500

    docs: Add sassc to the flatpak manifest example

 doc/build-howto.md | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)
---
diff --git a/doc/build-howto.md b/doc/build-howto.md
index 36b0544a..a2941dfb 100644
--- a/doc/build-howto.md
+++ b/doc/build-howto.md
@@ -48,10 +48,32 @@ Then add Libadwaita as a git submodule:
 git submodule add https://gitlab.gnome.org/GNOME/libadwaita.git subprojects/libadwaita
 ```
 
-To bundle the library with your Flatpak application, add the following module to
+To bundle the library with your Flatpak application, add the following modules to
 your manifest:
 
 ```json
+{
+  "name" : "libsass",
+  "buildsystem" : "meson",
+  "sources" : [
+    {
+      "type" : "git",
+      "url" : "https://github.com/lazka/libsass.git";,
+      "branch" : "meson"
+    }
+  ]
+},
+{
+  "name" : "sassc",
+  "buildsystem" : "meson",
+  "sources" : [
+    {
+      "type" : "git",
+      "url" : "https://github.com/lazka/sassc.git";,
+      "branch" : "meson"
+    }
+  ]
+},
 {
   "name" : "libadwaita",
   "buildsystem" : "meson",