Packaging: Add requirements directly to setup.y

[mofe23]

Thx for creating release 1.2.0! Because requirements.txt was not packaged. unfortunately it failed with:

Traceback (most recent call last):
        File "<string>", line 2, in <module>
        File "<pip-setuptools-caller>", line 34, in <module>
        File "/tmp/pip-install-rnlvhfzw/googlesearch-python_6c9c2c2bfceb4afbafbe911906746a5f/setup.py", line 6, in <module>
          with open("requirements.txt") as fh:
      FileNotFoundError: [Errno 2] No such file or directory: 'requirements.txt'

The easiest way to fix this is to add requirements directly to setup.py - that's what this PR contains.

[Nv7-GitHub]

I used the method detailed in #47 instead, but thank you for the pull request!