updating rust package documentation

crates/linker/src/lib.rs

@@ -1,3 +1,8 @@
+//! Surgical linker that links platforms to Roc applications. We created our own 
+//! linker for performance, since regular linkers add complexity that is not 
+//! needed for linking Roc apps. Because we want `roc` to manage the build 
+//! system and final linking of the executable, it is significantly less 
+//! practical to use a regular linker.
 use memmap2::{Mmap, MmapMut};
 use object::Object;
 use roc_build::link::{rebuild_host, LinkType};