Disable password auth, mention rM2 ed25519 issue

Fixes #38

README.md

@@ -12,7 +12,7 @@ reMarkable screen sharing over SSH.
 1. Clone this repository: `git clone https://github.com/rien/reStream`.
 2. Install `lz4` on your host with your usual package manager. On Ubuntu,
 `apt install liblz4-tool` will do the trick.
-3. [Set up an SSH key and add it to the ssh-agent](https://help.github.com/en/github/authenticating-to-github/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent), then add your key to the reMarkable with `ssh-copy-id [email protected]`.
+3. [Set up an SSH key and add it to the ssh-agent](https://help.github.com/en/github/authenticating-to-github/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent), then add your key to the reMarkable with `ssh-copy-id [email protected]`. **Note:** the reMarkable 2 doesn't support `ed25519` keys, those users should generate and `rsa` key.
 4. Copy the `restream` executable to the reMarkable and make it executable.
     ```
     # scp restream.arm.static [email protected]:/home/root/restream

reStream.sh

@@ -78,12 +78,14 @@ done
 
 ssh_cmd() {
     echo "[SSH]" "$@" >&2
-    ssh -o ConnectTimeout=1 "$ssh_host" "$@"
+    ssh -o ConnectTimeout=1 -o PasswordAuthentication=no "$ssh_host" "$@"
 }
 
 # check if we are able to reach the remarkable
 if ! ssh_cmd true; then
-    echo "$ssh_host unreachable"
+    echo "$ssh_host unreachable or you have not set up an ssh key."
+    echo "If you see a 'Permission denied' error, please visit"
+    echo "https://github.com/rien/reStream/#installation for instructions."
     exit 1
 fi