Update docs.md

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[TD-12461]<fix>: Potential monitor crash when saving master uptime info into log database

Add maxRegexStringLen  explaination.

Add more explaination for join query.

remove one chapter

remove some chapters.

fix some typo.

Remove some words.

add more explaination on log files.

add taoslog use manual.

add gcc version suggestion for compiling udf.

Update docs.md

[no merge]test for CHANGE_FORK

[TD-11094][TD-6677][TD-10789][TD-12389]<test>:add taosdemo shell test case

[TD-12344]<test> add test case for coredump when session