Fix commit according to PR review

Changed so cargo specifies the binary collector, removing the need to
link to its local binary. Clarified that the SHAs should be from the
rustc-repo, but the command should be ran in the rustc-perf repo.

Author: Mattias-Petersson

src/profiling/with_rustc_perf.md

@@ -34,15 +34,15 @@ To start, in the `rustc-perf` repo, build the collector, which runs the Rust com
 ```
 cargo build --release -p collector
 ```
-After this the collector can be located in `.\target\release\collector`, can be run locally with `bench_local` and expects the following arguments:
+The collector can then be run using cargo, specifying the collector binary. It expects the following arguments:
 - `<PROFILE>`: Profiler selection for how performance should be measured. For this example we will use Cachegrind.
 - `<RUSTC>`: The Rust compiler revision to benchmark, specified as a commit SHA from `rust-lang/rust`.
 Optional arguments allow running profiles and scenarios as described above. `--include` in `x perf` is instead `--exact-match`. More information regarding the mandatory and
 optional arguments can be found in the [rustc-perf-readme-profilers].
 
-Then, for the case of generating a profile diff for the crate `serve_derive-1.0.136`, for two commits `<SHA1>` and `<SHA2>` in the `rust-lang/rust` repository, run the following
+Then, for the case of generating a profile diff for the crate `serve_derive-1.0.136`, for two commits `<SHA1>` and `<SHA2>` from the `rust-lang/rust` repository, run the following in the `rustc-perf` repo (where the collector was built in the previous step):
 ```
-./target/release/collector profile_local cachegrind +<SHA1> --rustc2 +<SHA2> --exact-match serde_derive-1.0.136 --profiles Check --scenarios IncrUnchanged
+cargo run --release --bin collector profile_local cachegrind +<SHA1> --rustc2 +<SHA2> --exact-match serde_derive-1.0.136 --profiles Check --scenarios IncrUnchanged
 ```