Uselect is not implemented

[nnn112358]

Uselect is not implemented in Maixpy

1. Uselect is blank page in Maixpy documentation.

https://maixpy.sipeed.com/en/libs/standard/uselect.html

2. MaixPy help does not show uselect in help().

MaixPy help('modules') KPU gc random uio Maix hashlib re ujson main heapq sensor ulab _boot image socket uos _thread json struct urandom _webrepl lcd sys ure array machine time usocket audio math touchscreen ustruct binascii math ubinascii utime board micropython ucollections utimeq builtins modules ucryptolib uzlib cmath nes uctypes video collections network uerrno zlib errno os uhashlib fpioa_manager pye_mp uheapq