feat: add preview command (#203)

- Add a new `sesh preview` command
- Add configuration support for the preview command

Author: danitrap

README.md

@@ -111,7 +111,7 @@ In order to integrate with tmux, you can add a binding to your tmux config (`tmu
 
 ```sh
 bind-key "T" run-shell "sesh connect \"$(
-  sesh list --icons | fzf-tmux -p 55%,60% \
+  sesh list --icons | fzf-tmux -p 80%,70% \
     --no-sort --ansi --border-label ' sesh ' --prompt '⚡  ' \
     --header '  ^a all ^t tmux ^g configs ^x zoxide ^d tmux kill ^f find' \
     --bind 'tab:down,btab:up' \
@@ -121,6 +121,8 @@ bind-key "T" run-shell "sesh connect \"$(
     --bind 'ctrl-x:change-prompt(📁  )+reload(sesh list -z --icons)' \
     --bind 'ctrl-f:change-prompt(🔎  )+reload(fd -H -d 2 -t d -E .Trash . ~)' \
     --bind 'ctrl-d:execute(tmux kill-session -t {2..})+change-prompt(⚡  )+reload(sesh list --icons)' \
+    --preview-window 'right:55%' \
+    --preview 'sesh preview {}'
 )\""
 ```
 
@@ -222,9 +224,14 @@ mkdir -p ~/.config/sesh && touch ~/.config/sesh/sesh.toml
 
 The default session can be configured to run a command when connecting to a session. This is useful for running a dev server or starting a tmux plugin.
 
+Additionally, you can define a preview command that runs when previewing the session's directory. This can be handy for displaying files with tools like [eza](https://github.com/eza-community/eza) or [lsd](https://github.com/lsd-rs/lsd).
+
+Note: The `{}` will be automatically replaced with the session's path.
+
 ```toml
 [default_session]
 startup_command = "nvim -c ':Telescope find_files'"
+preview_command = "eza --all --git --icons --color=always {}"
 ```
 
 If you want to disable the default start command on a specific session, you can set `disable_startup_command = true`.
@@ -235,7 +242,9 @@ A startup command is a command that is run when a session is created. It is usef
 
 **Note:** If you use the `--command/-c` flag, then the startup script will not be run.
 
-I like to use a command that opens nvim on session startup:
+I like to use a command that opens nvim on session startup.
+
+You can also define a preview command to display the contents of a specific file using [bat](https://github.com/sharkdp/bat) or any another file previewer of your choice.
 
 ```toml
 [[session]]
@@ -247,6 +256,7 @@ startup_command = "ls"
 name = "tmux config"
 path = "~/c/dotfiles/.config/tmux"
 startup_command = "nvim tmux.conf"
+preview_command = "bat --color=always ~/c/dotfiles/.config/tmux/tmux.conf"
 ```
 
 ### Listing Configurations