Add some basic instructions for building the BasicMinimalApi project locally

src/BenchmarksApps/BasicMinimalApi/BuildingLocally.md

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+# Building Locally
+
+When experimenting with possible improvements, it can be useful to be able to build this project locally.
+
+## Setup
+
+You're going to need a fairly recent version of dotnet (for both basic functionality and accurate baselining).
+One way to set that up is to download a [nightly build](https://github.com/dotnet/installer#table) and extract it into a local folder.
+(You can also install it, since dotnet handles side-by-side installation, but this can get cluttered if you install a lot of nightlies.)
+To use the nightly build you've extracted, you'll want to add the folder where you extracted it to the `PATH` and also set it as the `DOTNET_ROOT`.
+On Windows, a batch file for setting these variables might look like
+
+```
+@echo off
+set PATH=c:\dotnet;%PATH%
+set DOTNET_ROOT=c:\dotnet\
+```
+
+In order to avoid interfering with your other uses of dotnet, it's probably preferable to set those variables only in the prompt where you're building this project.
+
+Confirm that things are working by running `dotnet --version` - the output should match the build that you downloaded.
+Tools like `which` and `where` can also help confirm that you're running the version you expect.
+
+## Building
+
+In a prompt with `PATH` and `DOTNET_ROOT` set appropriately, run the following command
+```
+dotnet publish /p:PublishAot=true /p:StripSymbols=true /p:EnableRequestDelegateGenerator=true
+```
+The properties and their values come from the `basicminimalapipublishaot` scenario in [goldilocks.benchmarks.yml](../../../scenarios/goldilocks.benchmarks.yml).
+
+The build should complete without errors.
+
+## Validating
+
+Run `BasicMinimalApi` from the `publish` directory - something like `bin\Release\net8.0\win-x64\publish`.
+You should be able to connect to the server at http://localhost:5000/todos.
+(It will return a JSON blob.)
+
+## Experimenting
+
+As you make changes to your local `aspnetcore` build, you can pull those changes into the benchmark project by adding explicit references to the [csproj file](./BasicMinimalApi.csproj).
+```xml
+<ItemGroup>
+  <Reference Include="e:\aspnetcore\artifacts\bin\Microsoft.AspNetCore\Release\net8.0\Microsoft.AspNetCore.dll" />
+</ItemGroup>
+```