Remove shell prompt from installation CLI code (#3962)

GitHub's readme markdown rendering adds a button which allows
a user to copy the CLI into their copy cache to then paste into
a terminal and run.

Currently as the curl command contains a dollar sign, that gets
included (which means the user needs to manually remove it).

Really not a big deal and if this is closed I won't be upset,
but noted it's been a bit of a nit to me a few times.

Signed-off-by: Luke Hinds <lhinds@redhat.com>

README.md

@@ -32,7 +32,7 @@ The Wasmtime CLI can be installed on Linux and macOS with a small install
 script:
 
 ```sh
-$ curl https://wasmtime.dev/install.sh -sSf | bash
+curl https://wasmtime.dev/install.sh -sSf | bash
 ```
 
 Windows or otherwise interested users can download installers and