Missing top level README

[erights]

I notice that https://github.com/google/caja does have a home page. Should this have been automatically converted to a top-level README by the code.google -> github conversion tool?

[kpreid]

There's no automated conversion. But you're right, we should have a README. Unfortunately, lots of the intro text we have is semi-obsolete ("The Caja Compiler..." — we're not any sort of compiler any more.)

[jasvir]

I know that the text there isn't entirely accurate but I just created a PR for #1987 - lets get something up and we can correct it rather than having nothing at all.