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

pages/common/numfmt.md

@@ -0,0 +1,15 @@
+# numfmt
+
+> Convert numbers to and from human-readable strings.
+
+- Convert 1.5K (SI Units) to 1500:
+
+`numfmt --from={{si}} {{1.5K}}`
+
+- Convert 5th field (1-indexed) to IEC Units without converting header:
+
+`ls -l | numfmt --header={{1}} --field={{5}} --to={{iec}}`
+
+- Convert to IEC units, pad with 5 characters, left aligned:
+
+`du -s * | numfmt --to={{iec}} --format={{"%-5f"}}`