Feature request: Input yaml from stdin

[kgtkr]

Example:

# Input from stdin
$ openapi-typescript -

Currently openapi-typescript /dev/stdin doesn't work.

file:///home/kgtkr/path/to/node_modules/openapi-typescript/bin/cli.js:38
  throw new Error(errorMessage);
        ^

Error: ❌ Could not find any specs matching "/dev/stdin". Please check that the path is correct.
    at errorAndExit (file:///home/kgtkr/path/to/node_modules/openapi-typescript/bin/cli.js:38:9)
    at main (file:///home/kgtkr/path/to/node_modules/openapi-typescript/bin/cli.js:149:5)