Correct the build and run instructions in the README

[mikelangmayr]

• the documented cmake invocations did not work: cmake .. fails with You must specify -DCONTROLLER=, and the ARC column used -DINTERFACE_TYPE=AstroCam, which is not an option this project defines
• -DINSTRUMENT= was undocumented despite being needed to build an instrument module
• camerad <file.cfg> --foreground exits 1; the config is passed with --config, and there is no -d flag, since daemonizing is the default without --foreground
• the emulator takes -i <instrument>, and its note referred to INTERFACE_TYPE and claimed an Archon default that does not exist
• run_unit_tests is excluded from the default target, so it has to be built before it can be run
• documents that logging always goes to a daily file under LOGPATH, that stderr logging follows --foreground, and that LOG_STDERR overrides it
• every corrected command was run: bare cmake fails as described, the old camerad form exits 1, the new one starts and fills the daily log, and LOG_STDERR flips console output both ways
• documentation only, no code changes