coreutils commands: move pages to common/ folder (#2442)

pages/common/nl.md

@@ -0,0 +1,23 @@
+# nl
+
+> A utility for numbering lines, either from a file, or from standard input.
+
+- Number non-blank lines in a file:
+
+`nl {{file}}`
+
+- Read from standard output:
+
+`cat {{file}} | nl {{options}} -`
+
+- Number only the lines with printable text:
+
+`nl -t {{file}}`
+
+- Number all lines including blank lines:
+
+`nl -b a {{file}}`
+
+- Number only the body lines that match a basic regular expression (BRE) pattern:
+
+`nl -b p'FooBar[0-9]' {{file}}`