Base: Add a man page about pledge(2)

Base/usr/share/man/man2/pledge.md

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+## Name
+
+pledge - reduce process capabilities
+
+## Synopsis
+
+```**c++
+#include <unistd.h>
+
+int pledge(const char* promises, const char* execpromises);
+```
+
+## Description
+
+`pledge()` makes a promise to the kernel that from this moment on, it will only use a subset of system functionality.
+
+Functionality is divided into a curated set of promises (described below), which can be combined to cover the program's needs. Both arguments are space-separated lists of promises.
+
+Note that `pledge()` can be called repeatedly to remove previously-pledged promises, but it can never regain capabilities once lost.
+
+`promises` are applied to the current process, and will also be inherited by children created by [`fork`(2)](fork.md).
+
+`execpromises` are applied if/when a new process image is created with [`exec(2)`](exec.md).
+
+If `promises` or `execpromises` is null, the corresponding value is unchanged.
+
+## Promises
+
+* `stdio`: Basic I/O, memory allocation, information about self, various non-desctructive syscalls
+* `thread`: The POSIX threading API
+* `id`: Ability to change UID/GID
+* `tty`: TTY related functionility
+* `proc`: Process and scheduling related functionality
+* `exec`: The [`exec(2)`](exec.md) syscall
+* `tty`: TTY related functionility
+* `unix`: UNIX local domain sockets
+* `inet`: IPv4 domain sockets
+* `rpath`: "Read" filesystem access
+* `wpath`: "Write" filesystem access
+* `cpath`: "Create" filesystem access
+* `dpath`: Creating new device files
+* `chown`: Changing file owner/group
+* `fattr`: Changing file attributes/permissions
+* `shared_buffer`: Shared memory buffers
+* `chroot`: The [`chroot(2)`](chroot.md) syscall
+* `video`: May use [`ioctl(2)`](ioctl.md) and [`mmap(2)`](mmap.md) on framebuffer video devices
+
+## Errors
+
+* `EFAULT`: `promises` and/or `execpromises` are not null and not in readable memory.
+* `EINVAL`: One or more invalid promises were specified.
+* `EPERM`: An attempt to increase capabilities was rejected.