Update swagger instructions (#398)

## 🎟️ Tracking

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## 📔 Objective

Simplify the instructions by using the script that is now part of the
server repo: bitwarden/server#6066

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- Written new unit and / or integration tests where applicable
- Protected functional changes with optionality (feature flags)
- Used internationalization (i18n) for all UI strings
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- Updated any necessary documentation (Confluence, contributing docs) or
informed the documentation
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Author: dani-garcia

README.md

@@ -69,14 +69,10 @@ need to build the internal swagger documentation.
 
 ### Swagger generation
 
-The first step is to generate the swagger documents from the server repository.
+The first step is to generate the swagger documents from the root of the server repository.
 
 ```bash
-# src/Api
-dotnet swagger tofile --output ../../api.json ./bin/Debug/net8.0/Api.dll internal
-
-# src/Identity
-ASPNETCORE_ENVIRONMENT=development dotnet swagger tofile --output ../../identity.json ./bin/Debug/net8.0/Identity.dll v1
+pwsh ./dev/generate_openapi_files.ps1
 ```
 
 ### OpenApi Generator