Add yarn 😻

Author: spences10

README.md

@@ -5,3 +5,6 @@ A place for all my cheat sheets to live!
 - **[Git](git.md#useful-git-commands)**
 
 - **[npm](npm.md#npm-plz)**
+
+- **[Yarn](yarn.md#useful-yarn-commands)**
+

yarn.md

@@ -0,0 +1,21 @@
+# Useful Yarn commands
+
+This is just stuff that I have put down that I find I use a lot of the time for my own reference.
+
+## Update dependencies 
+
+```
+yarn upgrade
+```
+
+## displays the location of the yarn bin folder.
+
+```
+yarn bin
+```
+
+## list installed packages.
+
+```
+yarn ls
+```