Fix Build From Source example (#56105)

Author: sebastienros

docs/BuildFromSource.md

@@ -59,10 +59,13 @@ The steps you follow next depend on your preferred development environment:
     ./restore.cmd
     ```
 
-1. You'll typically focus on one project in the repo. You can use the `startvs.cmd` command to launch Visual Studio in a particular project area. For example, to launch Visual Studio in the `Components` project:
+1. You'll typically focus on one project in the repo. You can use the `startvs.cmd` command to launch Visual Studio in a particular project area. For example, to launch Visual Studio in the `src/Http` project, after you have built it with `./build.cmd`:
+
+    > :bulb: The `build.cmd` script will be local to the directory of the project you opened. For example, the script located in the `src/Http` directory. If you want to build the whole tree, use the `build.cmd` that is located in the `eng` directory.
 
     ```powershell
-    cd src\Components
+    cd src/Http
+    ./build.cmd
     ./startvs.cmd
     ```