Add examples of bsc flags I use (#949)

* Add examples of bsc flags I use

* Elaborate on open flag

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Co-authored-by: Florian Verdonck <[email protected]>

Author: nojaf

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

@@ -192,6 +192,8 @@ 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. `ABC` can either be a dependency, namespaced project or local module of the current project.
+
 ## gentypeconfig
 
 To enable genType, set `"gentypeconfig"` at top level in the project's `rescript.json`.