[evince] Fix formatting CONTRIBUTING.md

[Germán Poo-Caamaño <gpoo src gnome org>]

commit 951bde388fa17707097050b39d91f7e58b8ca6ef
Author: Germán Poo-Caamaño <gpoo gnome org>
Date:   Tue Jun 30 22:49:18 2020 +0000

    Fix formatting CONTRIBUTING.md

 CONTRIBUTING.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index e806bcc5..2c8b8fb5 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -152,8 +152,8 @@ Closes #1234
  second newline, but that is not nice for the interfaces).
 
  - Whenever possible, the first line should include the subsystem of
-   the evince the commit belongs: `shell`, `libdocument`, libview`,
-   `libmisc`, `backends`, `cut-n-paste`, `build`, `flatpak`.
+   the evince the commit belongs: `shell`, `libdocument`, `libview`,
+   `libmisc`, `backends`, `cut-n-paste`, `build`, `doc`, `flatpak`.
    e.g. “flatpak: bump version of poppler”
 
  - First line (the brief description) must only be one sentence and