Yarn: Error adding remote tarball package

yarn-error.log file:

Arguments: 
  /usr/bin/nodejs /usr/bin/yarn add https://github.com/blikblum/cherrytree/releases/download/svelte-2.4.2/build.tar.gz

PATH: 
  /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/snap/bin

Yarn version: 
  0.23.2

Node version: 
  6.10.2

Platform: 
  linux x64

npm manifest: 
  {
    "name": "testproj",
    "version": "1.0.0",
    "main": "index.js",
    "license": "MIT"
  }

yarn manifest: 
  No manifest

Lockfile: 
  No lockfile

Trace: 
  Error: https://github.com/blikblum/cherrytree/releases/download/svelte-2.4.2/build.tar.gz: EISDIR: illegal operation on a directory, open '/usr/local/share/.cache/yarn/v1/.tmp/9417ab587e459fe380a7e913f4160254/'
      at Error (native)

Hey, I struggled with this error for a while when I finally managed to find the root cause, at least in my case:

For a .tar.gz to be used by yarn add it must have the file names starting with a ./. I checked your tarball and all files are listed without the leading local directory ref (tar -tf build.tar.gz).

This can be fixed simply by modifying how you refer to your files when calling tar command (i.e. passing "./*" instead of "*"). Or if you're creating it programmatically, change the file names in the headers.

Thanks. That worked. Leaving open since at least a note in documentation is in order

Hey guys,
I have added a warning which informs the user of this behavior and suggests the solution.
Created PR #4898 for the same

This is my first contribution to yarn so please let me know if I have missed something. Thanks.