[#10459] 📝 Update documentation to use yarn --cwd arg

Signed-off-by: LvffY <louberger@hotmail.fr>

docs/getting-started/configuration.md

@@ -65,10 +65,9 @@ to install and configure the client.
 Stop Backstage, and go to the root directory of your freshly installed Backstage
 App. Use the following commands to start the PostgreSQL client installation:
 
-```shell
+```bash
 # From your Backstage root directory
-cd packages/backend
-yarn add pg
+yarn add --cwd packages/backend pg
 ```
 
 Use your favorite editor to open `app-config.yaml` and add your PostgreSQL

docs/getting-started/homepage.md

@@ -28,10 +28,9 @@ Now, let's get started by installing the home plugin and creating a simple homep
 
 #### 1. Install the plugin
 
-```
-# From your Backstage application directory
-cd packages/app
-yarn add @backstage/plugin-home
+```bash
+# From your Backstage root directory
+yarn add --cwd packages/app @backstage/plugin-home
 ```
 
 #### 2. Create a new HomePage component

docs/getting-started/running-backstage-locally.md

@@ -67,8 +67,8 @@ terminal windows, both starting from the Backstage project root.
 In the first window, run
 
 ```bash
-cd packages/backend
-yarn start
+# From your Backstage root directory
+yarn start --cwd packages/backend
 ```
 
 That starts up a backend instance on port 7007.