Add basic overview of Org mode syntax to the Vim doc

doc/org.txt

@@ -26,13 +26,83 @@ Org mode plugin -- that is what Emacs is for.
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  2. INSTALLATION                                                  *org-install*
 
-WIP.
+Installation of Org.vim can be performed by using your favourite Vim
+plugin/package management tool(s).
 
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  3. BASIC SYNTAX                                                   *org-syntax*
 
-WIP.
+Outline mode isn't used much anymore, one place it is still used is for GNU
+Emacs release notes.  It contains only a single piece of syntax: heading
+levels denoted by asterisks.
+>
+    * This is a heading
 
+    The first heading is equivalent to <h1> tags in HTML files.
+
+    ** This is a sub-heading
+
+    This heading uses 2 asterisks to denote that it is a below the previous
+    heading.
+
+    *** This is a sub-sub-heading
+
+    * This is another top level heading
+
+    Org.vim supports as many heading levels as you want, and each of these
+    headings can use Vim's folding keys and fold navigation.
+<
+Org mode is a huge superset of Outline mode. It uses the same heading syntax
+mentioned above, but supports many, many more features.  Org.vim supports the
+core subset of Org mode syntax, which should be suitable for most use cases.
+
+The following is a short overview of essential Org mode syntax.
+>
+    Org mode supports *bold*, /italic/, _underline_ and +strikethrough+ text
+    which is delimited by asterisks, forward-slashes, underscores, and pluses
+    respectively.
+
+    Paragraphs are separated by empty lines.
+
+    =monospaced= and ~verbatim~ text are delimited by equals signs and tilde
+    respectively.
+
+    : Entire lines can be marked as verbatim by prepending with a colon.
+
+    # Comments are lines prepended with a hash.
+
+    This is a link to the Org.vim repository [[https://github.com/axvr/org.vim]]
+
+    This is also a link to the [[https://github.com/axvr/org.vim][Org.vim repository]]
+    where the text "Org.vim repository" is the title of the link (link text).
+
+    - This is an item in a list.
+    - This is another item in the same list.
+      - This is a sub-item for the above list item.
+        - This is a sub-item for the previous list item.
+    + List items can also be denoted by using a plus sign
+    1. Or by numbering each item.
+    2. Like so.
+      - [ ] List items can also have checkboxes by using open and closing
+            square brackets.
+      - [X] By placing an uppercase X in between the square brackets you can
+            mark the item as "done".
+<
+Org.vim supports a lot more of Org mode's vast syntax than was mentioned here.
+You can learn much more of Org mode's syntax online.
+
+When Org.vim is installed, files ending with the extension `.org` will
+automatically have syntax highlighting and folding support enabled.  It can
+also be manually enabled with the following command.
+>
+    :set filetype=org
+<
+Outline mode doesn't have a file extension like Org mode so you will have to
+enable it manually. This is simply done by opening the file and runing the
+following command.
+>
+    :set filetype=outline
+<
 ==============================================================================
  4. CONFIGURATION                                           *org-configuration*
 
@@ -125,4 +195,4 @@ viewing the |license| section of the |uganda.txt| help doc from within Vim.
 [3]: <http://vimdoc.sourceforge.net/htmldoc/uganda.html#license>
 
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-vim:et:ts=8:sts=4:sw=4:tw=78:ft=help:norl:
+vim:et:ts=4:sts=4:sw=4:tw=78:ft=help:norl: