fix link in benchmark readme (#1176)

Author: kevinAlbs

benchmark/README.md

@@ -1,4 +1,4 @@
-This suite implements the benchmarks described in this spec: https://docs.google.com/document/d/1x7dCHHx_owOFYIPZ6VQwPerSWRhdkMSiepyFrNSFlLw/edit#
+This suite implements the benchmarks described in this spec: https://github.com/mongodb/specifications/blob/master/source/benchmarking/benchmarking.md
 
 # Compiling
 Configure the C++ driver to build with C++17 or newer and build the `microbenchmarks` target.
@@ -29,4 +29,4 @@ used.
 At this point, bson_decoding has not been added to the benchmarking suite due to the fact that
 extended_bson has not been added to the C++ driver (CXX-1241).
 
-Also note that the BSONBench tests are implemented to mirror the C driver's interpretation of the spec.
+Also note that the BSONBench tests are implemented to mirror the C driver's interpretation of the spec.