docs: update nuxt.md (#804)

Expanded on the TailwindCSS installation instructions.
The added information is important because from time to time the Nuxt module installation throws the following error:
```bash
$ npx nuxi@latest module add tailwindcss

 ERROR  [GET] "https://npm.fontawesome.com/@nuxtjs/tailwindcss/latest": 401 Unauthorized                                              8:39:48 a.m.

  at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
  at async $fetch2 (/C:/Users/ryanr/AppData/Local/npm-cache/_npx/b95349761371180e/node_modules/nuxi/dist/shared/nuxi.b88e7b0f.mjs:340:15)
  at async resolveModule (/C:/Users/ryanr/AppData/Local/npm-cache/_npx/b95349761371180e/node_modules/nuxi/dist/chunks/add2.mjs:262:15)
  at async Object.setup (/C:/Users/ryanr/AppData/Local/npm-cache/_npx/b95349761371180e/node_modules/nuxi/dist/chunks/add2.mjs:136:15)
  at async runCommand$1 (/C:/Users/ryanr/AppData/Local/npm-cache/_npx/b95349761371180e/node_modules/nuxi/dist/shared/nuxi.3e201632.mjs:1620:5)
  at async runCommand$1 (/C:/Users/ryanr/AppData/Local/npm-cache/_npx/b95349761371180e/node_modules/nuxi/dist/shared/nuxi.3e201632.mjs:1639:11)
  at async runCommand$1 (/C:/Users/ryanr/AppData/Local/npm-cache/_npx/b95349761371180e/node_modules/nuxi/dist/shared/nuxi.3e201632.mjs:1639:11)
  at async runMain$1 (/C:/Users/ryanr/AppData/Local/npm-cache/_npx/b95349761371180e/node_modules/nuxi/dist/shared/nuxi.3e201632.mjs:1777:7) 
```
Manually installing the package and then adding to the config fixes this issue.

apps/www/src/content/docs/installation/nuxt.md

@@ -33,6 +33,22 @@ npm install -D typescript
 npx nuxi@latest module add @nuxtjs/tailwindcss
 ```
 
+Alternatively, you can manually add `@nuxtjs/tailwindcss` using your dependency manager
+
+```bash
+npm install --save-dev @nuxtjs/tailwindcss
+```
+
+and then to the `modules` section of `nuxt.config.{ts,js}`
+
+```ts
+export default defineNuxtConfig({
+  modules: [
+    '@nuxtjs/tailwindcss'
+  ]
+})
+```
+
 ### Add `Nuxt` module
 
 <br>