Describe path-based and ID-based links in the README

README.md

@@ -18,10 +18,39 @@ The graph refreshes automatically every time you:
 ## Concepts
 
 - Title is always the first markdown heading of depth 1, i.e. `# Title`.
-- Any link or reference to a local file causes the extension to attempt parsing it. The title is required but links are optional (it results in a lone node with no edges in such case).
-- Graph is not directed. It doesn't show which file has the link and which one is linked.
+- Files which do not have a title do not appear in the graph
+- Files can link to other files usin path-based or ID-based links
+- The graph is not directed. It doesn't show which file has the link and which one is linked.
 - Directory structure is not relevant for the graph. All that matters is the mutual links between files.
 
+### Path-based links
+
+Regular markdown links syntax with a relative or absolute file. For example: `[link name](./other-file-in-this-dir.md)`.
+
+### ID-based links
+
+A file can be given an ID. The ID is a first string matching a configured pattern (see Settings) found in the file.
+
+File having an ID can be linked using double-bracketed ("wiki-style") links. For example:
+
+```md
+<!-- file1.md -->
+
+# This is a file having an id
+
+This is its id: 20200522225822
+```
+
+```md
+<!-- file2.md -->
+
+# This is a file linking to another
+
+See the other file: [[20200522225822]]
+```
+
+This feature is heavily inspired by [Zettlr](https://github.com/Zettlr/Zettlr), therefore its [documentation](https://docs.zettlr.com/en/reference/settings/#the-id-regex) may give useful background.
+
 ## Examples
 
 Here are some examples to better explain the above.
@@ -58,6 +87,10 @@ Controls in which column should the graph appear. Refer to [Column values](###co
 
 Controls in which column should clicked files open. Refer to [Column values](###column-values). Defaults to `one`.
 
+### `markdown-links.fileIdRegexp`
+
+A [regular expression](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions) used to find the file id for use in wiki-style links.
+
 ### Column values
 
 - `active` – in the currently focused column.