docs: Update SDK root in README

[goonerify]

Command line tools path seems to have changed from $ANDROID_SDK_ROOT/cmdline-tools/tools to $ANDROID_SDK_ROOT/cmdline-tools/cmdline-tools

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[rigor789]

The reason I haven't merged this yet, is that I couldn't confirm the path is correct - since both on Windows & macOS these don't exist (cmdline-tools) and are located at <SDK_ROOT>/tools/bin