Make note about "./blink1-tool" vs "blink1-tool" in docs

[todbot]

[from email with JP] In Linux/Mac OS X, you generally don't have (and it's bad practice) to put the current directory ('.') in the PATH. Therefore, if you're building and using blink1-tool from source, you may want to do this:

cd blink1/commandline
make 
blink1-tool

but this will result in "command not found". Instead the last line should be:

./blink1-tool

Alternatively, you could also do:

cd blink1/commandline
make
sudo make install
blink1-tool

because then blink1-tool gets installed globally.

Finally, consider putting into the Makefile a target for installing udev rules for most common Linux targets (Ubuntu & Raspbian)

h/t @jedgarpark