docs: specify version in v1 installation guide

Author: mbledkowski

docs/content-v1/en/1.getting-started/2.installation.md

@@ -7,11 +7,11 @@ Add `@nuxt/content` dependency to your project:
 
 ::code-group
   ```bash [Yarn]
-  yarn add @nuxt/content
+  yarn add @nuxt/content@^1
   ```
 
   ```bash [NPM]
-  npm install @nuxt/content
+  npm install @nuxt/content@^1
   ```
 ::