Fix link to manual and reference.md (#216)

* Fix link to manual

* Fix link to reference.md

(not sure how useful this is, because the page appears to be an autogen stub, but currently the link is 404)

Author: ihnorton

README.md

@@ -30,9 +30,9 @@ pkg> add BenchmarkTools
 
 ## Documentation
 
-If you're just getting started, check out the [manual](doc/manual.md) for a thorough explanation of BenchmarkTools.
+If you're just getting started, check out the [manual](docs/src/manual.md) for a thorough explanation of BenchmarkTools.
 
-If you want to explore the BenchmarkTools API, see the [reference document](doc/reference.md).
+If you want to explore the BenchmarkTools API, see the [reference document](docs/src/reference.md).
 
 If you want a short example of a toy benchmark suite, see the sample file in this repo ([benchmark/benchmarks.jl](benchmark/benchmarks.jl)).