fix(file-templates): update doom doc templates

To reflect the new mode: line added in 7e400ab, and add an ID property.
Also corrects heading level in __doom-readme file template.

Ref: 7e400abdc0

modules/editor/file-templates/templates/org-mode/__doom-docs

@@ -1,6 +1,10 @@
 # -*- mode: snippet -*-
 # name: Doom documentation
 # --
+# -*- mode: doom-docs-org -*-
+:PROPERTIES:
+:ID:       `(doom-docs-generate-id)`
+:END:
 #+title:    ${1:Title}
 #+subtitle: ${2:Subtitle}