Warn user about unsupported pull-syntax inside posh queries

[theronic]

Could Posh please warn the user when they try to pull inside a p/q posh query?

I lost two days trying to figure out why my ClojureScript threw Assert failed: (db? db) when posh does not support the pull syntax inside posh queries. It says so in the README - I've read it before. I knew this information, but I forgot. It was especially hard to debug from a React Native app where the error for using a pull query inside q looks like this:

[jamesnyika]

@theronic - I hear you man. I lost a week! But what I did to begin mitigating this kind of timewasting was to start my own documentation wiki in my repo. I began to document important lessons I learned as I build my application - specifically for things like this which are important reminders that are easy to forget. It then cuts down my context switching when I return to the code particularly after longer absences. That way I keep the lessons close to the codebase where I learned them. It is really slow moving but that is how I am paying the debt!

[mpdairy]

Oh sorry, ya'll! I've been out of the Clojure world for some time (using Haskell) and didn't see this issue. Do you want it to give a runtime warning or maybe I could just make it bold in the Readme?

[theronic]

Runtime warning would be best :)