[docs] Update docs: kernel mem, process init

Updated documentation: Added documentation on the kernel address space
layout, process initialization, and rebuilt the syscall docs.

docs/process_initialization.rst

@@ -0,0 +1,42 @@
+.. jsix process initialization in userspace
+
+Process Initialization
+======================
+
+jsix follows the `System V ABI`_ on the ``amd64`` architecture. All arguments
+needed for program initialization are passed to the program's initial thread on
+the stack.
+
+Note that jsix adds a number of additional auxiliary vector entry types for
+passing jsix-specific data to a program. The jsix-specific auxiliary vector type
+codes (what the ABI document refers to as ``a_type``) start from ``0xf000``. See
+the header file ``<j6/init.h>`` for more detail.
+
+.. _System V ABI: https://gitlab.com/x86-psABIs/x86-64-ABI
+
+The initial stack frame
+-----------------------
+
+==============  ====================  ============  =======
+Address         Value                 Bytes         Notes
+==============  ====================  ============  =======
+``top``                                             Stack top (out of stack bounds)
+``top`` - 16    0                     16            Stack sentinel
+\               ``envp`` string data  ?
+\               ``argv`` string data  ?
+\               ...                   ?             Possible padding
+\               0, 0 (``AT_NULL``)    16            Aux vector sentinel
+\               Aux vectors           16 * `m`      ``AT_NULL``-terminated array of Aux vectors
+\               0                     8             Environment sentinel
+\                ``envp``             8 * `n`       0-terminated array of environment
+                                                    string pointers
+\               0                     8             Args sentinel
+\               ``argv``              8 * ``argc``  Pointers to argument strings
+``rsp``         ``argc``              8             Number of elements in argv
+==============  ====================  ============  =======
+
+
+* :ref:`genindex`
+* :ref:`search`
+
+