add sha1sum, sha224sum, sha256sum, sha384sum, and sha512sum pages

pages/linux/sha256sum.md

@@ -0,0 +1,13 @@
+# sha256sum
+
+> Calculate SHA256 cryptographic checksums
+
+- Calculate the SHA256 checksum for file(s) or files in a directory, one checksum per file
+
+`sha256sum {{filename1}}`
+`sha256sum {{filename1}} {{filename2}}`
+`sha256sum {{directory/\*}}`
+
+- Read a file of SHA256 sums and verify all files have matching checksums
+
+`sha256sum -c {{filename.sha256}}`