Convert mkShell from DocBook to CommonMark

doc/builders/special.xml

@@ -6,5 +6,5 @@
   This chapter describes several special builders.
  </para>
  <xi:include href="special/fhs-environments.xml" />
- <xi:include href="special/mkshell.xml" />
+ <xi:include href="special/mkshell.section.xml" />
 </chapter>

doc/builders/special/mkshell.section.md

@@ -0,0 +1,15 @@
+# pkgs.mkShell {#sec-pkgs-mkShell}
+
+`pkgs.mkShell` is a special kind of derivation that is only useful when using it combined with `nix-shell`. It will in fact fail to instantiate when invoked with `nix-build`.
+
+## Usage {#sec-pkgs-mkShell-usage}
+
+```nix
+{ pkgs ? import <nixpkgs> {} }:
+pkgs.mkShell {
+  # this will make all the build inputs from hello and gnutar
+  # available to the shell environment
+  inputsFrom = with pkgs; [ hello gnutar ];
+  buildInputs = [ pkgs.gnumake ];
+}
+```

doc/builders/special/mkshell.xml

@@ -1,24 +0,0 @@
-<section xmlns="http://docbook.org/ns/docbook"
-         xmlns:xlink="http://www.w3.org/1999/xlink"
-         xmlns:xi="http://www.w3.org/2001/XInclude"
-         xml:id="sec-pkgs-mkShell">
- <title>pkgs.mkShell</title>
-
- <para>
-  <function>pkgs.mkShell</function> is a special kind of derivation that is only useful when using it combined with <command>nix-shell</command>. It will in fact fail to instantiate when invoked with <command>nix-build</command>.
- </para>
-
- <section xml:id="sec-pkgs-mkShell-usage">
-  <title>Usage</title>
-
-<programlisting><![CDATA[
-{ pkgs ? import <nixpkgs> {} }:
-pkgs.mkShell {
-  # this will make all the build inputs from hello and gnutar
-  # available to the shell environment
-  inputsFrom = with pkgs; [ hello gnutar ];
-  buildInputs = [ pkgs.gnumake ];
-}
-]]></programlisting>
- </section>
-</section>