dos: add platform, dos/cd: add page (#18375)

CONTRIBUTING.md

@@ -74,6 +74,7 @@ The `pages` directory and `pages.*` language-specific directories contain the pl
 
 - `android`: Android
 - `cisco-ios`: Cisco IOS
+- `dos`: MS-DOS/DOSBox/FreeDOS
 - `freebsd`: FreeBSD
 - `openbsd`: OpenBSD
 - `osx`: OSX/Mac OS/macOS (will be replaced by `macos`)

README.md

@@ -55,7 +55,7 @@ How about:
 
 This repository is just that: an ever-growing collection of examples
 for the most common UNIX, Linux, macOS, FreeBSD, NetBSD, OpenBSD,
-SunOS, Android, Windows, and Cisco IOS command-line tools.
+SunOS, Android, Windows, Cisco IOS, and DOS command-line tools.
 
 ## How do I use it?
 

pages/dos/cd.md

@@ -0,0 +1,16 @@
+# CD
+
+> Change the current working directory.
+> More information: <https://www.gnu.org/software/bash/manual/bash.html#index-cd>.
+
+- Go to the specified directory:
+
+`CD {{PATH\TO\DIRECTORY}}`
+
+- Go up to the parent of the current directory:
+
+`CD ..`
+
+- Go to the root directory of the current drive:
+
+`CD \`