[swift-inspect] update README.md for Linux CMake build

Author: andrurogerz

tools/swift-inspect/README.md

@@ -32,6 +32,15 @@ In order to build on Windows with CMake, some additional parameters must be pass
 cmake -B out -G Ninja -S . -D ArgumentParser_DIR=... -D CMAKE_Swift_FLAGS="-Xcc -I%SDKROOT%\usr\include\swift\SwiftRemoteMirror"
 ~~~
 
+In order to build on Linux with CMake, some additional parameters must be passed to the build tool to locate the necessary Swift modules.
+
+~~~
+cmake -B out -G Ninja -S . -D ArgumentParser_DIR=... -D CMAKE_Swift_FLAGS="-Xcc -I$(git rev-parse --show-toplevel)/include/swift/SwiftRemoteMirror"
+~~~
+
+Building with CMake requires a local copy of [swift-argument-parser](https://github.com/apple/swift-argument-parser) built with CMake.
+The `ArumentParser_DIR=` definition must refer to the `cmake/modules` sub-directory of the swift-argument-parser build output directory.
+
 ### Using
 
 The following inspection operations are available currently.