docs: Add section on constants to tutorial

Author: brson

doc/tutorial.md

@@ -463,6 +463,41 @@ character, such as `\n`, `\r`, and `\t`. String literals,
 written between double quotes, allow the same escape sequences. Rust strings
 may contain newlines.
 
+## Constants
+
+Compile-time constants are declared with `const`. All scalar types,
+like integers and floats, may be declared `const`, as well as fixed
+length vectors, static strings (more on this later), and structs.
+Constants may be declared in any scope and may refer to other
+constants. Constant declarations are not type inferred, so must always
+have a type annotation.  By convention they are written in all capital
+letters.
+
+~~~
+// Scalars can be constants
+const MY_PASSWORD: int = 12345;
+
+// Scalar constants can be combined with other constants
+const MY_DOGGIES_PASSWORD: int = MY_PASSWORD + 1;
+
+// Fixed-length vectors
+const MY_VECTORY_PASSWORD: [int * 5] = [1, 2, 3, 4, 5];
+
+// Static strings
+const MY_STRINGY_PASSWORD: &static/str = "12345";
+
+// Structs
+struct Password {
+    value: int
+}
+
+const MY_STRUCTY_PASSWORD: Password = Password { value: MY_PASSWORD };
+~~~
+
+> ***Note:*** Support for compile-time constants and constant
+> evaluation is essentially added 'as needed'. You may find that
+> things you expect to work do not.
+
 ## Operators
 
 Rust's set of operators contains very few surprises. Arithmetic is done with