Add examples of bsc flags I use

Author: Florian Verdonck

pages/docs/manual/latest/build-configuration.mdx

@@ -192,6 +192,9 @@ The warning numbers are shown in the build output when they're triggered. See [W
 
 Extra flags to pass to the compiler. For advanced usages.
 
+- `-open ABC` opens the module `ABC` for each file in the project.
+- `-w -45` enable or disable certain compiler warnings. In this example, `-45` means to disable warning number 45.
+
 ## gentypeconfig
 
 To enable genType, set `"gentypeconfig"` at top level in the project's `rescript.json`.