docs: update local build instructions

Clarify the need to install dependencies before building to ensure `tailwindcss` is available.
Offer `npm ci` as the preferred reproducible install method and `npm install` as an alternative.

Co-authored-by: PR0M3TH3AN <[email protected]>

README.md

@@ -103,8 +103,14 @@ To run **bitvid** locally:
 
 2. Install dependencies:
 
+   If you cloned the repo but haven’t run `npm install`/`npm ci`, `npx` won’t find the local `tailwindcss`.
+
    ```bash
+   # reproducible install (preferred for CI / locks)
    npm ci
+
+   # or if you want to install/upgrade packages
+   npm install
    ```
 
 3. Build the project: