Build Chinese vesions of pdf fail

[王听正]

I modified file name in parseBook.py to README-ch.md:

for folder in folders:
    if os.path.isfile(folder + '/README.md'):
        with open(folder + '/README.md', "r") as originalChapter:
            fileString = originalChapter.read()

but I got lots of error after I run make clean pdf

[WARNING] Missing character: There is no 你 in font [lmroman10-regular]:mapping=tex-text;!

Chinese character is not supported by lmroman10-regular font, How can I change font?