feat(rtx) Added new polyglot runtime manager (asdf rust clone) (#11932)

* add readme.md for rtx
* add rtx plugin
* update install info
* remove redundant slashes

plugins/rtx/rtx.plugin.zsh

@@ -0,0 +1,30 @@
+# Find where rtx should be installed
+RTX_DIR="${RTX_DIR:-$HOME/.rtx}"
+RTX_COMPLETIONS="$RTX_DIR/completions"
+
+if [[ ! -f "$RTX_DIR/rtx.sh" || ! -f "$RTX_COMPLETIONS/_rtx" ]]; then
+  # If not found, check for archlinux/AUR package (/opt/rtx-vm/)
+  if [[ -f "/opt/rtx-vm/rtx.sh" ]]; then
+    RTX_DIR="/opt/rtx-vm"
+    RTX_COMPLETIONS="$RTX_DIR"
+  # If not found, check for Homebrew package
+  elif (( $+commands[brew] )); then
+    _RTX_PREFIX="$(brew --prefix rtx)"
+    RTX_DIR="${_RTX_PREFIX}/libexec"
+    RTX_COMPLETIONS="${_RTX_PREFIX}/share/zsh/site-functions"
+    unset _RTX_PREFIX
+  else
+    return
+  fi
+fi
+
+# Load command
+if [[ -f "$RTX_DIR/rtx.sh" ]]; then
+  source "$RTX_DIR/rtx.sh"
+  # Load completions
+  if [[ -f "$RTX_COMPLETIONS/_rtx" ]]; then
+    fpath+=("$RTX_COMPLETIONS")
+    autoload -Uz _rtx
+    compdef _rtx rtx # compdef is already loaded before loading plugins
+  fi
+fi