fix: Updates SSH command to use PEM format

[megaconfidence]

The example command in the docs uses the OPENSSH format which is not supported by Caprover and leads to deployment issues. This PR updates the example comand to use the PEM format.

[githubsaturn]

@megaconfidence - thanks for the PR. But what makes you think that this format is not supported by CapRover?

It's been the recommended format since a few years ago. See this:
caprover/caprover#1265 (comment)

[megaconfidence]

@githubsaturn I've been trying to set up CapRover for two days straight, and was blocked by this issue

The docs clearly state only the PEM format is supported, but then goes on to give an example using the unsupported OPENSSH format, which lead to my blocker. I could have concluded the product was broken and dropped off at that point, but I was able to figure my way out

I raised this PR so that the next person doesn't have to bang their head on the wall

[githubsaturn]

ed25519 is the cipher, PEM is the format.

But that's weird that you generated a key pair using ed25519 and it didn't work. I'll be more than happy to take a look at it.

Would you mind creating a key pair using the exiting command in the docs and upload it somewhere so I can look at it?

Just to be confirm, you're using this key just for the purpose of deploying from github, right?