add basic docs

docs/plugins.md

@@ -0,0 +1,14 @@
+# Plugins
+
+## Getting started
+
+Plugins are stored in .juci/plugins
+
+### Basic hello world
+from Jucipp import Terminal
+
+print("Hello world from before the application is loaded")
+
+def init_hook():
+    t = Terminal()
+    t.print("Hello, world! From after the application is started.")