remove "yarn_old" bs from readme

- it was created by me for local dev / backup original asdf-yarn
  so it is irrelevant for other people

README.md

@@ -10,48 +10,14 @@ Yarn plugin for the [mise][https://mise.jdx.dev/] version manager.
 This plugin should work out of the box on Linux and Mac operating systems.
 If one of the commands needed is unavailable, it will let you know.
 
-## Installing
+## Installing / Updating
 
 ```
 mise plugin i yarn
 ```
 
-## Migration from twuni/asdf-yarn
-
-### Issue with yarn_old
-If you can't update plugin like this
-```bash
-$ mise plugins update yarn
-mise plugin:yarn is a symlink, not updating
-```
-
-Try removing both yarn and yarn_old
-```bash
-$ mise plugins rm yarn
-$ mise plugins rm yarn_old
-```
-
-And then try to install newer version
-```bash
-$ mise plugins i yarn
-mise plugin:yarn ✓ https://github.com/mise-plugins/asdf-yarn.git#somehash
 ```
-
-if instead it outputs that it still installs from `twuni/asdf-yarn` like
-``` bash
-mise plugin:yarn ✓ https://github.com/twuni/asdf-yarn.git#somehash
-```
-
-then your registry is still not updated. You can set it to update more frequently (atm there is no command in mise to force update registry) and try to reinstall
-```bash
-$ mise settings set plugin_autoupdate_last_check_duration 1h
-$ mise plugins rm yarn
-$ mise plugins i yarn
-```
-
-it should output
-```bash
-mise plugin:yarn ✓ https://github.com/mise-plugins/asdf-yarn.git#somehash
+mise plugin up yarn
 ```
 
 # Development