Update benchmarking docs

docs/src/performance.md

@@ -106,7 +106,22 @@ resulting performance improvements of Trixi.jl are given in the following blog p
 We use [PkgBenchmark.jl](https://github.com/JuliaCI/PkgBenchmark.jl) to provide a standard set of
 benchmarks for Trixi.jl. The relevant benchmark script is
 [benchmark/benchmarks.jl](https://github.com/trixi-framework/Trixi.jl/blob/main/benchmark/benchmarks.jl).
-You can run a standard set of benchmarks via
+To benchmark the changes made in a PR, please proceed as follows:
+
+1. Check out the latest `main` branch of your Trixi.jl development repository.
+2. Check out the latest development branch of your PR.
+3. Change your working directory to the `benchmark` directory of Trixi.jl.
+4. Execute `julia run_benchmarks.jl`.
+
+This will take some hours to complete. When everything is finished, some
+output files will be created in the `benchmark` directory of Trixi.jl.
+
+!!! note
+    Please note that the benchmark scripts use `--check-bounds=no` at the moment.
+    Thus, they will not work in any useful way for Julia v1.10 (and newer?), see
+    [Julia issue #50985](https://github.com/JuliaLang/julia/issues/50985).
+
+You can also run a standard set of benchmarks manually via
 ```julia
 julia> using PkgBenchmark, Trixi