I am following the link http://ubuntutechnical.wordpress.com...tom-man-pages/
for adding an entry in man pages..
But this procedure does not include any modification in kernel source...

So is this a OS dependent work? (ie. what I want to know is that creating entries for different user functions, system calls , etc... is this done by the OS at install time, or when we install any application?)

Or we can implement it in kernel source itself?
Consider a scenario: I am making system calls and then implementing it in the kernel, and compiling and re installing the new kernel.. System calls work fine. So now I want to add a manual entry for my system call. Do I have to explicitly now enter the information in man pages using the tutorial above , or is there a way to add it in kernel documentation itself...
I hope I am clear..

The advantage of creating man pages is that they can be installed along with an application and accessed by users. Only kernel developers have access to the kernel source or see the kernel Documentation.

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You include info in ../Documentation the same way you include source in the kernel tree - using a patch.
To get that included in the shipped kernel means submitting it to the maintainer of that branch of the tree. That also means obeying the agreed coding standards/layout requirements. This is not an insignificant undertaking of itself - in addition to the coding. All covered in the ../Documentation.

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