README: Fix the order of sources/libraries in example compilation commands.

Some linkers (among them, the GNU ld 2.28 on my laptop, which clang
relies on for linking) are picky about the order they get their
ingredients in on the command line.  When they are, they want the
leaf nodes (like your `main` function) first, and the dependencies
(like `libcompiler.a`) after.

It's kind of counterintuitive (at least to me) that this is the
preferred order, though I can understand it from the perspective
of efficient resource use in the era when some linkers were first
written.  Anyway, it's the way it is.  There's a detailed
explanation here:
  https://stackoverflow.com/a/409470/378130

So, adjust the examples in the README to an order that should
work everywhere.

This fixes part of #102.

README.md

@@ -137,8 +137,8 @@ To create the parser, compile this file like this:
 clang++ -std=c++11 \
   -I tree-sitter/include \
   -L tree-sitter/out/Release \
-  -l compiler \
   arithmetic_grammar.cc \
+  -l compiler \
   -o arithmetic_grammar
 ```
 
@@ -209,8 +209,8 @@ To demo this parser's capabilities, compile this program like this:
 clang \
   -I tree-sitter/include \
   -L tree-sitter/out/Debug \
+   test_parser.c arithmetic_parser.c \
   -l runtime \
-  arithmetic_parser.c test_parser.c \
   -o test_parser
 
 ./test_parser