Replaces tomato emoji with GitHub flavored markdown

[snehankekre]

The tomato emoji in the README breaks installation on Windows via setup.py:

with open("README.md", "r") as fh:
    long_description = fh.read()

PS C:\Users\sneha\Desktop> pip install plost --no-cache-dir
Collecting plost
  Downloading Plost-0.2.1.tar.gz (12 kB)
    ERROR: Command errored out with exit status 1:
     command: 'c:\users\sneha\appdata\local\programs\python\python38\python.exe' -c 'import io, os, sys, setuptools, tokenize; sys.argv[0] = '"'"'C:\\Users\\sneha\\AppData\\Local\\Temp\\pip-install-6oqzx1bp\\plost_026235d7f64b4ef5854eed7dffc9ce84\\setup.py'"'"'; __file__='"'"'C:\\Users\\sneha\\AppData\\Local\\Temp\\pip-install-6oqzx1bp\\plost_026235d7f64b4ef5854eed7dffc9ce84\\setup.py'"'"';f = getattr(tokenize, '"'"'open'"'"', open)(__file__) if os.path.exists(__file__) else io.StringIO('"'"'from setuptools import setup; setup()'"'"');code = f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' egg_info --egg-base 'C:\Users\sneha\AppData\Local\Temp\pip-pip-egg-info-qt103lso'
         cwd: C:\Users\sneha\AppData\Local\Temp\pip-install-6oqzx1bp\plost_026235d7f64b4ef5854eed7dffc9ce84\
    Complete output (7 lines):
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "C:\Users\sneha\AppData\Local\Temp\pip-install-6oqzx1bp\plost_026235d7f64b4ef5854eed7dffc9ce84\setup.py", line 4, in <module>
        long_description = fh.read()
      File "c:\users\sneha\appdata\local\programs\python\python38\lib\encodings\cp1252.py", line 23, in decode
        return codecs.charmap_decode(input,self.errors,decoding_table)[0]
    UnicodeDecodeError: 'charmap' codec can't decode byte 0x8d in position 4: character maps to <undefined>

Replaces the emoji with GitHub flavored markdown :tomato: so that the emoji is correctly rendered on GitHub + the README is parsed on Windows.