Update docs and gitignore

.gitignore

@@ -1,6 +1,6 @@
 .vscode
 .DS_Store
-pkcs11gn/pkcs11gn
+pkcs11gn
 *.deb
 *.sig
 *.gpg

CONTRIBUTING.md

@@ -12,7 +12,7 @@ Please submit new issues [here](https://github.com/volvo-cars/pkcs11-utils/issue
 
 Changes to the repository are managed through [pull requests](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/about-pull-requests).
 
-To open a pull request with a proposed change, fork the repository, make your changes and open a pull request. Please link pull requests to issues where applicable.
+To propose a change, fork the repository, make your changes and open a pull request. Please link pull requests to issues where applicable.
 
 
 ### Links

README.md

@@ -6,12 +6,25 @@ The tool is pronounced as "pee-kay-see-sign".
 
 # Usage
 
+This guide assumes that you have access to a configured [PIV-enabled YubiKey](https://developers.yubico.com/PIV/Introduction/YubiKey_and_PIV.html).
+In addition, you will need the [ykcs11 module](https://developers.yubico.com/yubico-piv-tool/YKCS11):
+```shell
+Linux: sudo apt install ykcs11
+Mac: brew install yubico-piv-tool
+Windows: https://developers.yubico.com/yubico-piv-tool/Releases
+```
+
 You need a to create a `~/.crypto11.json` such as [crypto11.config.yubikey](example/crypto11.config.yubikey)
-with `Path`, `SlotNumber` and optionally `Pin` and X509 `CommonName` to identify the key you want to use.
+with `Path`, `SlotNumber` and optionally `Pin` and X509 `CommonName` to identify the key you want to use. `CommonName`
+is only required if your YubiKey has more than one cert loaded onto it.
 
 The full set of configuration options is documented [here](https://pkg.go.dev/github.com/ThalesIgnite/crypto11#Config).
 The only undocumented field is `CommonName` as it is only needed by this tool.
 
+## Build
+Compile the binary
+`make pkcs11gn`
+
 ## Sign file
 
 The following will sign `file.bin` with the private key on the PKCS#11 device.