docs: update installation commands (#723)

As "Copy" button copies the whole content, `$ npm install ...` would copy the dollar sign too, but it's redundant and not a valid command to run. I removed it to keep consistent and provide the best UX for tanstack users.

Author: davletovalmir

docs/installation.md

@@ -9,25 +9,25 @@ Install your TanStack Virtual adapter as a dependency using your favorite npm pa
 ## React Virtual
 
 ```bash
-$ npm install @tanstack/react-virtual
+npm install @tanstack/react-virtual
 ```
 
 ## Solid Virtual
 
 ```bash
-$ npm install @tanstack/solid-virtual
+npm install @tanstack/solid-virtual
 ```
 
 ## Svelte Virtual
 
 ```bash
-$ npm install @tanstack/svelte-virtual
+npm install @tanstack/svelte-virtual
 ```
 
 ## Vue Virtual
 
 ```bash
-$ npm install @tanstack/vue-virtual
+npm install @tanstack/vue-virtual
 ```
 
 ## Lit Virtual
@@ -45,5 +45,5 @@ $ npm install @tanstack/angular-virtual
 ## Virtual Core (no framework)
 
 ```bash
-$ npm install @tanstack/virtual-core
+npm install @tanstack/virtual-core
 ```