improve CLI readme contribution part

Use php 8.1 with SDK generator, and 7.4 no longer works with SDK-generator.

Author: lohanidamodar

templates/cli/README.md.twig

@@ -95,7 +95,7 @@ $ cd sdk-generator
 $ docker run --rm --interactive --tty --volume "$(pwd)":/app composer install --ignore-platform-reqs --optimize-autoloader --no-plugins --no-scripts --prefer-dist
 
 # Generate the SDKs
-$ docker run --rm -v $(pwd):/app -w /app php:7.4-cli php example.php
+$ docker run --rm -v $(pwd):/app -w /app php:8.1-cli php example.php
 ```
 
 3. Head over to the generated SDK and install the dependencies.
@@ -115,4 +115,4 @@ $ {{ language.params.executableName|caseLower }} -v
 ```
 ## License
 
-Please see the [{{spec.licenseName}} license]({{spec.licenseURL}}) file for more information.
+Please see the [{{spec.licenseName}} license]({{spec.licenseURL}}) file for more information.