import time


with open('test.md', 'r+', encoding='utf-8') as md_file:
    md = md_file.read()
    print(md)
    
    md_file.write('hello action!')
    md_file.write(f'greeting from {time.time()}\n')
    date_time = time.strftime("%Y-%m-%d %H:%M:%S", time.localtime())
    md_file.write(date_time)
    md_file.write('\n')