docs: Document org-transclusion-html

docs/org-transclusion-manual.org

@@ -540,6 +540,24 @@ Example 5:
 #+transclude: [[./things-at-point-dir/baz.el::id:1234567890][barz-baz-fuzz]]  :src elisp :thingatpt defun
 #+end_example
 
+*** Transclude HTML content with Pandoc
+#+cindex: Transclude HTML content with Pandoc
+
+If you have Pandoc installed, you can transclude local HTML files
+as Org documents.
+
+This feature is provided as an [[#extensions][extension]] (default off).
+
+#+begin_example
+#+transclude: [[file:../test/source-html-no-ext]]
+#+end_example
+
+Since it's not currently possible to add anchor links to local =file:=
+Org links, HTML transclusions always render the entire document as
+Org.  However, packages which transclude HTML documents over a
+network, such as [[https://git.sr.ht/~ushin/hyperdrive.el][hyperdrive.el]] and [[https://git.sr.ht/~breatheoutbreathein/org-transclusion-http][org-transclusion-http]], are able to
+render specific HTML elements by tag.
+
 ** Extensions
 :PROPERTIES:
 :CUSTOM_ID: extensions
@@ -550,6 +568,7 @@ Example 5:
 #+cindex: Extension - org-transclusion-indent-mode
 #+cindex: Extension - org-transclusion-src-lines
 #+cindex: Extension - org-transclusion-font-lock
+#+cindex: Extension - org-transclusion-html
 
 Org-transclusion provides a simple extension framework, where you can use ~customize~ to selectively add new features.
 
@@ -577,6 +596,9 @@ Currently, the following extensions are available.
 - (on by default) ~org-transclusion-font-lock~ ::
   Add font-lock for =#+transclude=. Org mode's standard syntax treats the combination of a =#+transclude:= keyword and a link used by Org-transclusion as a keyword. This means it applies the ~org-meta-line~ face and the link part cannot be toggled as a normal link. This extension adds ~org-transclusion-keyword~ face to the keyword part and lets the link part to be treated as a normal link for ~org-toggle-link-display~.
 
+- (off by default) ~org-transclusion-html~ ::
+  Transclude local HTML files by converting them to Org with Pandoc.
+
 * Customizing
 
 #+vindex: org-transclusion-extensions