[gtk/doc-chapters-markdown] doc: Check for pandoc

[Matthias Clasen <matthiasc src gnome org>]

commit eb2c5d38e03ae54e030cd8e27b0b420c56f71e2b
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat May 23 21:41:15 2020 -0400

    doc: Check for pandoc
    
    Add an explicit check for pandoc, so we get a clear
    error message if it is missing.

 docs/reference/gtk/meson.build | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/docs/reference/gtk/meson.build b/docs/reference/gtk/meson.build
index b30bbb91b7..13b4072023 100644
--- a/docs/reference/gtk/meson.build
+++ b/docs/reference/gtk/meson.build
@@ -403,6 +403,8 @@ if get_option('gtk_doc')
   configure_file(input: 'version.xml.in', output: 'version.xml', configuration: version_conf)
   configure_file(input: 'getting_started.xml.in', output: 'getting_started.xml', configuration: src_dir_conf)
 
+  # gtk-markdown-to-docbook uses pandoc
+  pandoc = find_program('pandoc', required: true)
   expand_md = find_program('gtk-markdown-to-docbook')
   expand_md_targets = []
   foreach t : expand_content_md_files