Add documentation for VSM.

PURL-TYPES.rst

@@ -176,7 +176,6 @@ cpan
 - The ``namespace``:
   - To refer to a CPAN distribution name, the ``namespace`` MUST be present. In this case, the namespace is the CPAN id of the author/publisher. It MUST be written uppercase, followed by the distribution name in the ``name`` component. A distribution name may NEVER contain the string ``::``.
   - To refer to a CPAN module, the ``namespace`` MUST be absent. The module name MAY contain zero or more ``::`` strings, and the module name MUST NOT contain a ``-``
-
 - The ``name`` is the module or distribution name and is case sensitive.
 - The ``version`` is the module or distribution version.
 - Optional qualifiers may include:
@@ -579,6 +578,18 @@ swift
       pkg:swift/github.com/Alamofire/[email protected]
       pkg:swift/github.com/RxSwiftCommunity/[email protected]
 
+vsm
+---
+``vsm`` for Visual Studio Marketplace packages:
+
+- The default repository is: https://marketplace.visualstudio.com
+- The ``namespace`` is the organization and is case-sensitive.
+- The ``name`` is the package name and is case-sensitive.
+- The ``version`` is the package version.
+- Examples::
+
+    pkg:vsm/ms-vscode/[email protected]
+
 Other candidate types to define:
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~