docs: update linux command to include memory

### What does this PR do?

Adding --memory 6144 will help linux users set there ram to the required
minimum amount for the extension to work well.

### Screenshot / video of UI

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screenshots or screencasts showing the difference -->

N/A

### What issues does this PR fix or reference?

<!-- Include any related issues from Podman Desktop
repository (or from another issue tracker). -->

N/A

### How to test this PR?

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Signed-off-by: Charlie Drage <[email protected]>

README.md

@@ -151,7 +151,7 @@ Or set when initially creating a Podman Machine via Podman Desktop:
 On Linux, you are unable to create a Podman Machine through the GUI of Podman Desktop, to create a rootful Podman Machine you can run the following commands:
 
 ```sh
-podman machine init --rootful
+podman machine init --memory 6144 --rootful
 podman machine start
 ```