Add note that TypeScript's emitDecoratorMetadata flag is not supported

[dummdidumm]

I tried using tsyringe, a library using decorators for constructor dependency injection. To my surprise it did not work. After some digging I found out that the problem is that ESBuild, which is used by Snowpack to compile the code, does not support TypeScript's emitDecoratorMetadata flag, which in this case is needed. (this means inversify will likely suffer from the same problem)

I'm posting this here so others in the future can find the reason for the problem quicker. I also suggest to put a note about this into the snowpack docs about this.
In ideal world, this is implemented at some point in ESBuild, but several closed issues about this topic in that repo hint that this may never be the case.

[FredKSchott]

You can also use the Babel plugin to customize how Snowpack builds your JS, instead of our less customizable built-in esbuild-er.

[joswarmer]

Is this a general problem with typescript decorators? I am using mobx decorators and this does not seem to work either.