Add information about librt and OpenBSD to the FAQ

FAQ

@@ -92,9 +92,9 @@ Putting these lines into your .zshrc will fix the problems.
 
 ## I cannot compile st in OpenBSD
 
-OpenBSD lacks of librt, but it is mandatory in POSIX
+OpenBSD lacks of librt, despite it begin mandatory in POSIX
 <http://pubs.opengroup.org/onlinepubs/9699919799/utilities/c99.html#tag_20_11_13>.
-If you want compile st for OpenBSD you have to remove -lrt from config.mk, and
-st will compile without any loss of functionality because all the functions are
+If you want to compile st for OpenBSD you have to remove -lrt from config.mk, and
+st will compile without any loss of functionality, because all the functions are
 included in libc on this platform.