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/README.md

@@ -0,0 +1,30 @@
+## rtx
+
+
+Adds integration with [rtx](https://github.com/jdx/rtx), a runtime executor compatible with npm,  nodenv, pyenv, etc. rtx is written in rust and is very fast. 20x-200x faster than asdf. With that being said, rtx is compatible with asdf plugins and .tool-versions files. It can be used as a drop-in replacement.
+
+### Installation
+
+1. [Download & install rtx](https://github.com/jdx/rtx#installation) by running the following:
+
+  ```
+  curl https://rtx.pub/install.sh | sh
+  ```
+
+
+2. [Enable rtx](https://github.com/jdx/rtx#quickstart) by adding it to your `plugins` definition in `~/.zshrc`.
+
+  ```
+  plugins=(rtx)
+  ```
+
+### Usage
+
+See the [rtx readme](https://github.com/jdx/rtx#table-of-contents) for information on how to use rtx. Here are a few examples:
+
+```
+rtx install node         Install the current version specified in .tool-versions/.rtx.toml
+rtx use -g node@system   Use system node as global default
+rtx install node@20.0.0  Install a specific version number
+rtx use -g node@20       Use node-20.x as global default
+```