unlink: add page (#2324)

pages/common/unlink.md

@@ -0,0 +1,8 @@
+# unlink
+
+> Remove a link to a file from the filesystem.
+> The file contents is lost if the link is the last one to the file.
+
+- Remove the specified file if it is the last link:
+
+`unlink {{path/to/file}}`