add a bit more info to README.md

Author: BenjaminHinchliff

README.md

@@ -28,6 +28,25 @@ print("Hello world")
 ```
 ````
 
+### Gotcha(s)
+
+There are few things that you can't *really* do in this python interpreter. One thing is that printing is really weird. Printing is done to a local variable called `printed`, if you want to acess the output you'll have to do a top-level print. This is a side-effect of RestrictedPython.
+
+For example:
+```py
+def print_num(num):
+  print(num)
+  return printed
+
+print(print_num(num))
+```
+
+a bit awkward, I know, but there's not much I can do about  it.
+
+## Libraries
+
+It's on my mind, but I don't think it'll be possible without a much heaver layer of virtualization. Let me know if you have any ideas.
+
 ## My Attempts to Not Get Hacked
 
-So, I'm not naive, I know how dangerous this stuff is, so I haven't just plugged user input into an `eval` or something. I'm using the library `RestrictedPython` to provide a (hopefully) safe execution environment and set up a 10 second timeout to avoid hangups on infinite loops. I'm really hoping I didn't miss anything, but please email me if I did.
+So, I'm not naive, I know how dangerous this stuff is, so I haven't just plugged user input into an `eval` or something. I'm using the library `RestrictedPython` to provide a (hopefully) safe execution environment and set up a 10 second timeout to avoid hangups on infinite loops. I'm really hoping I didn't miss anything, but please open and issue if I did.