Add documentation regarding local and try build benchmarks.

Fixes #70.

Author: Mark-Simulacrum

collector/README.md

@@ -14,6 +14,29 @@ $RUSTC_TIMING should point to a clone of the `https://github.com/rust-lang-nurse
 repository. Optionally, `--sync-git` can be passed to make the collector sync with the remote repo
 before and after comitting.
 
+### Running locally
+
+Follow the standard instructions above, but run like this:
+
+```
+./target/release/collector --benchmarks collector/benchmarks --output-repo $RUSTC_TIMING \
+    bench_local $COMMIT_HASH $DATE $RUSTC
+```
+
+$RUSTC should point to the compiled rustc in stage1 or stage2, i.e.
+`./build/x86_64-unknown-linux-gnu/stage2/bin/rustc`. Stage 2 is likely a little better for
+benchmarking purposes, but not critical.
+
+Once this is done, you can run the site (`./target/release/site $RUSTC_TIMING`) and use the
+comparison page to compare the before/after runs.
+
+### @bors try builds
+
+Alternatively, you can ping `simulacrum` on IRC to run the benchmarks on the server for a try build.
+This, today, consists of running `bench_commit $COMMIT_HASH` for the try build, and will take
+around ~30 minutes once the try build completes. This is often the preferred approach, though does
+take longer than running locally (as you have to wait for the try build to complete on Travis).
+
 ## How it works
 
 We download the artifacts (rustc, rust-std, cargo) produced by CI and properly unarchive them into
@@ -28,3 +51,4 @@ x86_64-unknown-linux-gnu is supported, but the system should trivially expand to
 Will only work for commits that have builds on s3://rust-lang-ci/rustc-builds: these merged after
 rust-lang/rust#38748 (bors sha: 927c55d86b0be44337f37cf5b0a76fb8ba86e06c). Additionally, try builds
 can also be tested, but the process is currently manual.
+