feat: Rewrite default out text

This has been in place for a long time now, before we had an install
script, so it ended up repeating a bunch of the same things that the
install script does automatically. I rewrote it so that it gives more
helpful information about how you're supposed to do Rustlings.
Hopefully this will reduce the number of "I started Rustlings and it
gave me an error" issues (no offense to anyone who opened one of those,
it was pretty unclear that it _wasn't_ an error).

default_out.txt

@@ -1,19 +1,25 @@
 Thanks for installing Rustlings!
 
-Is this your first time?
+Is this your first time? Don't worry, Rustlings was made for beginners! We are
+going to teach you a lot of things about Rust, but before we can get
+started, here's a couple of notes about how Rustlings operates:
 
-Let's make sure you're up to speed:
-- You have Rust installed, preferably via `rustup`
-- You have `~/.cargo/bin` added to your PATH variable
-- You have cloned this repository (https://github.com/rust-lang/rustlings)
-- You have installed Rust language support for your editor
-- You have locally installed the `rustlings` command by running an
-  installation script or manually executing:
+1. The central concept behind Rustlings is that you solve exercises. These
+   exercises usually have some sort of syntax error in them, which will cause
+   them to fail compliation or testing. Sometimes there's a logic error instead
+   of a syntax error. No matter what error, it's your job to find it and fix it!
+   You'll know when you fixed it because then, the exercise will compile and
+   Rustlings will be able to move on to the next exercise.
+2. If you run Rustlings in watch mode (which we recommend), it'll automatically
+   start with the first exercise. Don't get confused by an error message popping
+   up as soon as you run Rustlings! This is part of the exercise that you're
+   supposed to solve, so open the exercise file in an editor and start your
+   detective work!
+3. If you're stuck on an exercise, there is a helpful hint you can view by typing
+   'hint' (in watch mode), or running `rustlings hint myexercise`.
+4. If an exercise doesn't make sense to you, feel free to open an issue on GitHub!
+   (https://github.com/rust-lang/rustlings/issues/new). We look at every issue,
+   and sometimes, other learners do too so you can help each other out!
 
-cargo install --force --path .
-
-If you've done all of this (or even most of it), congrats! You're ready
-to start working with Rust.
-
-To get started, run `rustlings watch` in order to get the first exercise.
-Make sure to have your editor open!
+Got all that? Great! To get started, run `rustlings watch` in order to get the first
+exercise. Make sure to have your editor open!