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

pages/common/sha256sum.md

@@ -0,0 +1,15 @@
+# sha256sum
+
+> Calculate SHA256 cryptographic checksums.
+
+- Calculate the SHA256 checksum for a file:
+
+`sha256sum {{filename1}}`
+
+- Calculate SHA256 checksums for multiple files:
+
+`sha256sum {{filename1}} {{filename2}}`
+
+- Read a file of SHA256 sums and verify all files have matching checksums:
+
+`sha256sum -c {{filename.sha256}}`