fix: makepkg, build user

README.md

@@ -4,8 +4,43 @@
 [![Docker Pulls](https://img.shields.io/docker/pulls/volkerraschek/build-image)](https://hub.docker.com/r/volkerraschek/build-image)
 
 This project contains all sources to build the container image
-`docker.io/volkerraschek/build-image`. The primary goal of the image is only
-to provide an environment to compile source code like go or rust.
+`docker.io/volkerraschek/build-image`. The primary goal of the image is only to
+provide an environment to compile source code for `go` or `rust` and package
+compiled binaries as PKG for Arch Linux or as RPM for RHEL based distributions.
+
+## Supported environment variables
+
+### gnupg
+
+#### GNUPG_KEY
+
+Import private gpg key via `GPG_KEY`. The private key must be escaped to import
+the key inside the container image correctly. For example:
+
+```bash
+GPG_FPR=YOUR_GPG_FINGERPRINT
+GPG_KEY=$(gpg --armor --export-secret-keys ${GPG_FPR} | cat -e | sed -e 's/\$/\\n/g' -e 's/^[ \t]*//g')
+```
+
+### makepkg
+
+The `makepkg.conf` configuration is composed from the environment variables with
+the prefix `MAKEPKG_`. Below are some examples:
+
+`MAKEPKG_PACKAGER="Hugo McKinnock <hugo.mckinnock@example.local>"`
+`MAKEPKG_GPGKEY="0123456789"`
+`MAKEPKG_PKGEXT=.pkg.tar.zst"`
+
+### ssh
+
+#### SSH_KEY
+
+Import private ssh key via `SSH_KEY`. The private key must be escaped to import
+the key inside the container image correctly. For example:
+
+```bash
+SSH_KEY=$(cat -e ${HOME}/.ssh/id_rsa | sed -e 's/\$/\\n/g')
+```
 
 ## Usage
 
@@ -22,6 +57,21 @@ $ docker run \
       go build
 ```
 
+### makepkg
+
+With the following example will be an package be build for Arch Linux. Execute
+the commond in the root directory of the project, where the `PKGBUILD` file is
+located.
+
+```bash
+$ docker run \
+    --env MAKEPKG_PACKAGER="Max Mustermann <max.mustermann@example.com" \
+    --rm \
+    --volume ${PWD}:/workspace \
+    volkerraschek/build-image:latest \
+      makepkg
+```
+
 ### rust
 
 If you want to compile instead go rust sourcecode, than you can do it similar to