Clarify how to run build script

Author: JanCBrammer

README.md

@@ -128,7 +128,7 @@ The easiest way to build any (or all) `InChI` sub-project(s) using `CMake` is to
 
 ##### Linux/macOS
 
-Run `./inchi_build_tool.sh`.
+Run `./inchi_build_tool.sh` from within the `INCHI-1-SRC` directory.
 
 *CMake build tool* users are only required to enter a number that corresponds to one or all `InChI` sub-projects which should be built from source using `CMake`.