Update lkl.txt

[miaomingc]

add needed build dependence in document
add help document about configuration

[tavip]

Thanks @miaomingc for updating the docs!

Please update your commit format to match kernel conventions:

lkl: update documentation

Add needed build dependency and information about how to change the  configuration.

Signed-off-by: Name <email>

[miaomingc]

@tavip thanks for suggestion ,check it again pls

[tavip]

Thanks @miaomingc, one more minor request, could you please remove the "Update lkl.txt" line from the commit, it is redundant now with the newly added "lkl: update documentation". Thanks!