README.rst is included in MANIFEST.in so that minimongo can be installed with pip

The PyPi package is broken, apparently because the package is missing the file `README.rst`.

When `minimongo` is installed with `pip install minimongo` this is the output

    pip install minimongo
    Downloading/unpacking minimongo
      Downloading minimongo-0.2.8.tar.gz
      Running setup.py egg_info for package minimongo
        Traceback (most recent call last):
          File "<string>", line 16, in <module>
          File "/private/var/folders/nx/b1h0sgls32d4p57q11msdq100000gn/T/pip_build_arialdomartini/minimongo/setup.py", line 58, in <module>
            long_description=LONG_DESCRIPTION,
        NameError: name 'LONG_DESCRIPTION' is not defined
        Complete output from command python setup.py egg_info:
        Traceback (most recent call last):
    
      File "<string>", line 16, in <module>
    
      File "/private/var/folders/nx/b1h0sgls32d4p57q11msdq100000gn/T/pip_build_arialdomartini/minimongo/setup.py", line 58, in <module>

        long_description=LONG_DESCRIPTION,
    
    NameError: name 'LONG_DESCRIPTION' is not defined
    
    ----------------------------------------
    Cleaning up...
    Command python setup.py egg_info failed with error code 1 in /private/var/folders/nx/b1h0sgls32d4p57q11msdq100000gn/T/pip_build_arialdomartini/minimongo
    Storing complete log in /Users/arialdomartini/.pip/pip.log


The file `README.rst` has been added in `MANIFEST.in` so that hopefully the next build will produce a working PyPi package