Improve the UX of README command codeblocks

* Removes the leading terminal prompt `$` from single command
  codeblocks, so that GitHub's "copy to clipboard" feature can be
  used to copy the commands directly into the terminal.
* Switches multi-line "command plus example output" codeblocks
  from language `shell` to `console` to prevent broken syntax
  highlighting (e.g. the "test" in "To test your buildpack" was being
  highlighted as a bash script, not console output).

README.md

@@ -30,8 +30,8 @@ be carried out once and don't need to be repeated for each buildpack you will wr
 Start by installing [libcnb-cargo](https://crates.io/crates/libcnb-cargo), which provides the `libcnb` Cargo command
 that we will use later to package our buildpack:
 
-```shell
-$ cargo install libcnb-cargo
+```
+cargo install libcnb-cargo
 ```
 
 #### Cross-compilation prerequisites
@@ -41,8 +41,8 @@ eventually run. This means we have to cross-compile our buildpack. The `libcnb p
 up your environment depending on your host platform, but we always need the appropriate target platform for Rust, which
 we can install with `rustup`:
 
-```shell
-$ rustup target add x86_64-unknown-linux-musl
+```
+rustup target add x86_64-unknown-linux-musl
 ```
 
 #### Docker
@@ -61,15 +61,14 @@ Find their documentation about installing it here: <https://buildpacks.io/docs/i
 After we've successfully set up our development environment, we can move on and create a new Rust project for our 
 buildpack. First, we create a new binary crate with Cargo:
 
-```shell
-$ cargo new my-buildpack
-     Created binary (application) `my-buildpack` package
+```
+cargo new my-buildpack
 ```
 
 Then, add the `libcnb` dependency to your project's `Cargo.toml`:
 
-```shell
-$ cargo add libcnb
+```
+cargo add libcnb
 ```
 
 Note: If you get an error about `cargo add` not being a supported command, make sure you are
@@ -177,7 +176,7 @@ your development environment, you have access to the `libcnb` Cargo command that
 
 In your project directory, run `cargo libcnb package` to start packaging:
 
-```shell
+```console
 $ cargo libcnb package
 🚚 Preparing package directory...
 🖥️ Gathering Cargo configuration (for x86_64-unknown-linux-musl)
@@ -208,7 +207,7 @@ You might have seen in the output that we're now ready to run our buildpack loca
 with `pack`. Before we can do this, we need an application to build. Since our buildpack does not interact with the
 application code at all, we just create an empty directory and use that as our application:
 
-```shell
+```console
 $ mkdir bogus-app
 $ pack build my-image --buildpack packaged/x86_64-unknown-linux-musl/debug/libcnb-examples_my-buildpack --path bogus-app --builder heroku/builder:22
 ...
@@ -241,7 +240,7 @@ Successfully built image my-image
 The newly created Docker image can be run in the same way as you would a Docker image created via `docker build`.
 If all went well, you should see our "Hello World!" message in your terminal:
 
-```shell
+```console
 $ docker run my-image
 Hello World!
 ```

libcnb-cargo/README.md

@@ -4,16 +4,16 @@ A Cargo command for managing buildpacks written with [libcnb.rs](https://github.
 
 ## Installation
 
-```shell
-$ cargo install libcnb-cargo
+```
+cargo install libcnb-cargo
 ```
 
 ## Usage
 
 Currently, there is only one sub-command: `package`. It allows users to package their
 Rust buildpack in a spec-compliant manner and helps with cross-compilation.
 
-```shell
+```console
 $ cargo libcnb package --help
 Packages a libcnb.rs Cargo project as a Cloud Native Buildpack
 
@@ -30,7 +30,7 @@ Options:
 Using it is fairly simple, run `cargo libcnb package` inside the buildpack's
 project directory:
 
-```shell
+```console
 $ cargo libcnb package
 🚚 Preparing package directory...
 🖥️ Gathering Cargo configuration (for x86_64-unknown-linux-musl)