libc: Document the functions in unistd.h

libs/libc/include/unistd.h

@@ -8,16 +8,29 @@ extern "C"
 {
 #endif
 
+    /* Not implemented. */
     int execv(const char*, char* const[]);
+    /* Not implemented. */
     int execve(const char*, char* const[], char* const[]);
+    /* Not implemented. */
     int execvp(const char*, char* const[]);
+    /* Not implemented. */
     pid_t fork(void);
-    long syscall(long, ...);
-    unsigned int sleep(unsigned int);
 
-    ssize_t read(int, void*, size_t);
+    /* Calls the kernel for a specific service, determined by number. */
-    ssize_t write(int, const void*, size_t);
+    long syscall(long number, ...);
-    int close(int);
+
+    /* Suspends execution for a chosen amount of seconds. */
+    unsigned int sleep(unsigned int seconds);
+
+    /* Reads count bytes from the file descriptor fd into the memory at buf. */
+    ssize_t read(int fd, void* buf, size_t count);
+
+    /* Writes count bytes of the memory at buf to the file descriptor fd. */
+    ssize_t write(int fd, const void* buf, size_t count);
+
+    /* Closes the file descriptor fd. */
+    int close(int fd);
 
 #ifdef __cplusplus
 }