Update preambles.mdx

Author: edwardalee

docs/writing-reactors/preambles.mdx

@@ -474,7 +474,7 @@ By having the `preamble` inside the reactor, you can define any functions or mac
 This will allow you to reuse code across different reactions easily within the same reactor.
 This also can allow us to change the scope of items using the `use` statement.
 
-For example, the follow reactor brings the constant `PI` into scope and print out the first 15 digits of pi:
+For example, the follow reactor brings the constant `PI` into scope and prints out the first 15 digits of pi:
 
 ```lf-rs
 target Rust;