Add imports chapter

Signed-off-by: trivernis <trivernis@protonmail.com>

chapters/imports.md

@@ -0,0 +1,40 @@
+# Imports
+
+A key feature of Snekdown is splitting a document
+into several files and importing those files in the main
+document.
+
+Additionally files that provide Glossary entries, Bibliography, Style and
+Configurations can be imported with the same syntax.
+
+```
+<[path]
+
+# import another snekdown document at the current position
+<[document.md]
+
+# import a stylesheet that will be embedded in the document
+<[style.css][type=stylesheet]
+
+# import a configuration file
+<[Manifext.toml]
+
+# import bibliography
+<[MyBib.toml][type=bibliography]
+
+# import a glossary
+
+<[MyGls.toml][type=glossary]
+```
+
+The parser differentiates five different types of imported files.
+
+- `document` - The default import which is just another Snekdown document
+- `stylesheet` - CSS Stylesheets that are included when rendering
+- `bibliography` - A file including bibliography
+- `config/manifest` - A config file that contains metadata
+- `glossary` - Glossary entries
+
+Imports of Snekdown documents are parsed in a separate thread, so you
+might see a performance improvement when splitting a large document into
+several files.

main.md

@@ -43,6 +43,10 @@
 
 - - -
 
+<[chapters/imports.md]
+
+- - -
+
 <[chapters/bibliography.md]
 
 - - -