copy subset of Sprig template functions

docs/sprig/crypto.md

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+# Cryptographic and Security Functions
+
+Sprig provides a couple of advanced cryptographic functions.
+
+## sha1sum
+
+The `sha1sum` function receives a string, and computes it's SHA1 digest.
+
+```
+sha1sum "Hello world!"
+```
+
+## sha256sum
+
+The `sha256sum` function receives a string, and computes it's SHA256 digest.
+
+```
+sha256sum "Hello world!"
+```
+
+The above will compute the SHA 256 sum in an "ASCII armored" format that is
+safe to print.
+
+## sha512sum
+
+The `sha512sum` function receives a string, and computes it's SHA512 digest.
+
+```
+sha512sum "Hello world!"
+```
+
+The above will compute the SHA 512 sum in an "ASCII armored" format that is
+safe to print.
+
+## adler32sum
+
+The `adler32sum` function receives a string, and computes its Adler-32 checksum.
+
+```
+adler32sum "Hello world!"
+```