Start pgpainless-cli usage guide

docs/source/index.rst

@@ -22,4 +22,5 @@ Contents
 
    ecosystem.md
    quickstart.md
+   pgpainless-cli/usage.md
    sop.md

docs/source/pgpainless-cli/usage.md

@@ -0,0 +1,78 @@
+# User Guide PGPainless-CLI
+
+The module `pgpainless-cli` contains a command line application which conforms to the
+[Stateless OpenPGP Command Line Interface](https://datatracker.ietf.org/doc/draft-dkg-openpgp-stateless-cli/).
+
+You can use it to generate keys, encrypt, sign and decrypt messages, as well as verify signatures.
+
+## Implementation
+
+Essentially, `pgpainless-cli` is just a very small composing module, which injects `pgpainless-sop` as a
+concrete implementation of `sop-java` into `sop-java-picocli`.
+
+## Build
+
+To build a standalone *fat*-jar:
+```shell
+$ cd pgpainless-cli/
+$ gradle shadowJar
+```
+
+The fat-jar can afterwards be found in `build/libs/`.
+
+To build a [distributable](https://docs.gradle.org/current/userguide/distribution_plugin.html):
+
+```shell
+$ cd pgpainless-cli/
+$ gradle installDist
+```
+
+Afterwards, an uncompressed distributable is installed in `build/install/`.
+To execute the application, you can call `build/install/bin/pgpainless-cli{.bat}`
+
+## Usage
+
+Hereafter, the program will be referred to as `pgpainless-cli`.
+
+```
+$ pgpainless-cli help
+Stateless OpenPGP Protocol
+Usage: pgpainless-cli [COMMAND]
+
+Commands:
+  help           Stateless OpenPGP Protocol
+  armor          Stateless OpenPGP Protocol
+  dearmor        Stateless OpenPGP Protocol
+  decrypt        Stateless OpenPGP Protocol
+  inline-detach  Stateless OpenPGP Protocol
+  encrypt        Stateless OpenPGP Protocol
+  extract-cert   Stateless OpenPGP Protocol
+  generate-key   Stateless OpenPGP Protocol
+  sign           Stateless OpenPGP Protocol
+  verify         Stateless OpenPGP Protocol
+  inline-sign    Stateless OpenPGP Protocol
+  inline-verify  Stateless OpenPGP Protocol
+  version        Stateless OpenPGP Protocol
+
+Exit Codes:
+   0   Successful program execution.
+   1   Generic program error
+   3   Verification requested but no verifiable signature found
+  13   Unsupported asymmetric algorithm
+  17   Certificate is not encryption capable
+  19   Usage error: Missing argument
+  23   Incomplete verification instructions
+  29   Unable to decrypt
+  31   Password is not human-readable
+  37   Unsupported Option
+  41   Invalid data or data of wrong type encountered
+  53   Non-text input received where text was expected
+  59   Output file already exists
+  61   Input file does not exist
+  67   Cannot unlock password protected secret key
+  69   Unsupported subcommand
+  71   Unsupported special prefix (e.g. "@env/@fd") of indirect parameter
+  73   Ambiguous input (a filename matching the designator already exists)
+  79   Key is not signing capable
+Powered by picocli
+```