config: Add docs for new base64sha256 func

website/source/docs/configuration/interpolation.html.md

@@ -80,12 +80,17 @@ The supported built-in functions are:
   * `base64encode(string)` - Returns a base64-encoded representation of the
     given string.
 
-  * `sha1(string)` - Returns a SHA-1 hash representation of the
-    given string.
+  * `base64sha256(string)` - Returns a base64-encoded representation of raw
+    SHA-256 sum of the given string.
+    **This is not equivalent** of `base64encode(sha256(string))`
+    since `sha256()` returns hexadecimal representation.
+
+  * `sha1(string)` - Returns a (conventional) hexadecimal representation of the
+    SHA-1 hash of the given string.
     Example: `"${sha1(concat(aws_vpc.default.tags.customer, "-s3-bucket"))}"`
 
-  * `sha256(string)` - Returns a SHA-256 hash representation of the
-    given string.
+  * `sha256(string)` - Returns a (conventional) hexadecimal representation of the
+    SHA-256 hash of the given string.
     Example: `"${sha256(concat(aws_vpc.default.tags.customer, "-s3-bucket"))}"`
 
   * `cidrhost(iprange, hostnum)` - Takes an IP address range in CIDR notation