userspace: add additional script documentation

We have several scripts used by the build system related
to generating code for system calls, privileged mode stacks,
kernel object metadata, and application shared memory
partitions. Add some overview documentation for each.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>

scripts/gen_priv_stacks.py

@@ -4,6 +4,23 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 
+"""
+Script to generate gperf tables mapping threads to their privileged mode stacks
+
+Some MPU devices require that memory region definitions be aligned to their
+own size, which must be a power of two. This introduces difficulties in
+reserving memory for the thread's supervisor mode stack inline with the
+K_THREAD_STACK_DEFINE() macro.
+
+Instead, the stack used when a user thread elevates privileges is allocated
+elsewhere in memory, and a gperf table is created to be able to quickly
+determine where the supervisor mode stack is in memory. This is accomplished
+by scanning the DWARF debug information in zephyr_prebuilt.elf, identifying
+instances of 'struct k_thread', and emitting a gperf configuration file which
+allocates memory for each thread's privileged stack and creates the table
+mapping thread addresses to these stacks.
+"""
+
 import sys
 import argparse
 import struct