docs: Update plugin installation commands

Signed-off-by: Sergey Shevchenko <sergeyshevchdevelop@gmail.com>

.changeset/honest-peas-guess.md

@@ -0,0 +1,7 @@
+---
+'@backstage/plugin-analytics-module-ga4': patch
+'@backstage/plugin-devtools-backend': patch
+'@backstage/plugin-linguist-backend': patch
+---
+
+Update plugin installation docs to be more consistent across documentations

plugins/analytics-module-ga4/README.md

@@ -9,7 +9,11 @@ This plugin contains no other functionality.
 ## Installation
 
 1. Install the plugin package in your Backstage app:
-   `cd packages/app && yarn add @backstage/plugin-analytics-module-ga4`
+
+```sh
+yarn add --cwd packages/app @backstage/@backstage/plugin-analytics-module-ga4
+```
+
 2. Wire up the API implementation to your App:
 
 ```tsx

plugins/devtools-backend/README.md

@@ -10,8 +10,7 @@ Here's how to get the DevTools Backend up and running:
 
    ```sh
    # From the Backstage root directory
-   cd packages/backend
-   yarn add @backstage/plugin-devtools-backend
+   yarn add --cwd packages/backend @backstage/plugin-devtools-backend
    ```
 
 2. Then we will create a new file named `packages/backend/src/plugins/devtools.ts`, and add the

plugins/linguist-backend/README.md

@@ -14,8 +14,7 @@ Here's how to get the backend up and running:
 
    ```sh
    # From the Backstage root directory
-   cd packages/backend
-   yarn add @backstage/plugin-linguist-backend
+   yarn add --cwd packages/backend @backstage/plugin-linguist-backend
    ```
 
 2. Then we will create a new file named `packages/backend/src/plugins/linguist.ts`, and add the