fix description about ziplist, the code is ok (#6318)
fix description about ziplist, the code is ok (#6318)

* fix description about ZIP_BIG_PREVLEN(the code is ok), it's similar to
antirez#4705

* fix description about ziplist entry encoding field (the code is ok),
the max length should be 2^32 - 1 when encoding is 5 bytes
charsyam/redis,ofirluzon/redis,PKRoma/redis,oranagra/redis,ctripcorp/redis,charsyam/redis,ctripcorp/redis,soloestoy/redis,antirez/redis,oranagra/redis,charsyam/redis,neomantra/redis,ofirluzon/redis,soloestoy/redis,PKRoma/redis,antirez/redis,ofirluzon/redis,antirez/redis,PKRoma/redis,yossigo/redis,PKRoma/redis,yossigo/redis,neomantra/redis,ctripcorp/redis,yossigo/redis,neomantra/redis,oranagra/redis,PKRoma/redis,ofirluzon/redis,ofirluzon/redis,antirez/redis,ctripcorp/redis,charsyam/redis,soloestoy/redis,soloestoy/redis,yossigo/redis,oranagra/redis,charsyam/redis,oranagra/redis,neomantra/redis,soloestoy/redis,neomantra/redis,yossigo/redis