Docs: Add uname(1) and uname(2) man pages

Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/3d558f47b04

Base/usr/share/man/man1/uname.md

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+## Name
+
+uname - print kernel information
+
+## Synopsis
+
+`uname [-s] [-n] [-r] [-m] [-a]`
+
+## Description
+
+Print information about the operating system, as reported by the `uname()`
+system call.
+
+## Options
+
+* `-s`: Print the system name
+* `-n`: Print the node name (hostname)
+* `-r`: Print the system release version
+* `-m`: Print the machine type
+* `-a`: Print all of the above
+
+## Examples
+
+```sh
+$ uname -sm
+Serenity i686
+```
+
+## See also
+
+* [`uname`(2)](../man2/uname.md)

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

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+## Name
+
+uname - retrieve information about the current kernel
+
+## Synopsis
+
+```**c++
+#include <sys/utsname.h>
+
+int uname(struct utsname* buf);
+```
+
+## Description
+
+Retrieves information about the current kernel and writes it into the `utsname`
+structure pointed to by `buf`.
+
+```**c++
+struct utsname {
+    char sysname[];
+    char nodename[];
+    char release[];
+    char version[];
+    char machine[];
+};
+```
+
+## Return value
+
+If successful, returns 0. Otherwise, returns -1 and sets `errno` to describe the error.
+
+## Errors
+
+* `EFAULT`: `buf` is not a writable address.
+
+## See also
+
+* [`uname`(1)](../man1/uname.md)