Clarify how to install a release

[qadzek]

The instructions in README.md on how to install from the master branch are clear:

git clone https://github.com/rvaiya/keyd
cd keyd
make && sudo make install
sudo systemctl enable --now keyd

However, if one prefers to install a stable release, instructions seem to be absent. I tried to run the following:

curl -o keyd.tar.gz -L https://github.com/rvaiya/keyd/archive/refs/tags/v2.5.0.tar.gz
tar xf keyd.tar.gz
cd keyd-2.5.0
make

The make command seems to succeed (a bin directory is created), but an error is still thrown: fatal: not a git repository (or any of the parent directories): .git. This error has come up before: #602

Thanks again for this magnificent tool.