Installation guide is missing from the documentation

The documentation (readme.rst) mentions the downloading aspect of the software and then immediately proceeds to describing usage but there is nothing about how to install it on various platforms. I think mentioning that the binaries can be downloaded from the releases page is not enough because the binary name is already different than what is used in the command examples in the usage (binary is named sops-v3.6.1.exe but in the usage examples sops is executed). Some might think that the binary is an installer which then installs this "sops" executable and adds it to the PATH but double clicking on the executable doesn't do anything, other than showing a command prompt for a millisecond with an output "Error: no file specified". Would probably be enough to specify in the documentation that (for Windows) the executable should be placed in an arbitrary folder, renamed to "sops.exe" and ensuring the folder is in the PATH environment variable.

Open readme.rst and compare the existing downloading and usage sections. Check the releases page naming described in the issue, then document how users install or place the binary on the relevant platforms, including the Windows rename and PATH steps; done means a new user can install the binary and follow the existing command examples.