README: -tiny does a bit more now

On my machine, garble itself goes from about 5.7MiB to about 4.8 MiB
when being built with `garble build` and `garble build -tiny`,
which is roughly a 16% decrease in size.
The 2-5% figure is dated at this point, as we do better than that now.

README.md

@@ -66,16 +66,17 @@ declaration, for example.
 With the `-tiny` flag, even more information is stripped from the Go binary.
 Position information is removed entirely, rather than being obfuscated.
 Runtime code which prints panics, fatal errors, and trace/debug info is removed.
-All in all, this can make binaries 2-5% smaller.
+Many symbol names are also omitted from binary sections at link time.
+All in all, this can make binaries about 15% smaller.
 
 With this flag, no panics or fatal runtime errors will ever be printed, but they
 can still be handled internally with `recover` as normal. In addition, the
 `GODEBUG` environmental variable will be ignored.
 
 Note that this flag can make debugging crashes harder, as a panic will simply
-exit the entire program without printing a stack trace, and all source code
+exit the entire program without printing a stack trace, and source code
-positions are set to line 1. Similarly, `garble reverse` is generally not useful
+positions and many names are removed.
-in this mode.
+Similarly, `garble reverse` is generally not useful in this mode.
 
 ### Speed