update README

README.md

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 # dockerfiles
+
+## tl;dr
+
+To build every image: `$ mage all`
+
+## xena/alpine
+
+My custom spin of [Alpine Linux][alpine-linux] for containers with runit as a
+process manager. This also starts syslog in every container and adds my custom
+repo whose apkbuilds are at https://github.com/Xe/aports.
+
+This is based on alpine edge. I can make a version based on a stable branch if
+there is interest however.
+
+## xena/go
+
+```ruby
+$gover = "1.9"
+$repo = "github.com/user/project"
+
+from "xena/go"
+
+def foldercopy(dir)
+  copy "#{dir}", "/root/go/src/#{$repo}/#{dir}"
+end
+
+def gobuild(pkg)
+  run "go build #{$repo}/#{pkg} && go install #{$repo}/#{pkg}"
+end
+
+[
+    # vendor dependencies first so any changes to them breaks the cache.
+    "vendor",
+    # common prefix for code that can be reused.
+    "pkg",
+    # internal packages for things like database helpers.
+    "internal",
+    # the binaries that get run
+    "cmd",
+    # any scripts or tools needed for building the program
+    "build",
+].each { |x| foldercopy x }
+
+gobuild "cmd/foobar"
+run "cp /go/bin/foobar /usr/local/bin/foobar"
+
+run "rm -rf /usr/local/go /go/pkg /go/bin"
+
+flatten
+
+workdir "/go/src/#{$repo}"
+cmd "/usr/local/bin/foobar"
+
+tag "user/project:latest"
+```
+
+## xena/go-mini
+
+### paths to delete when cleaning
+
+- /root/sdk
+- /root/go/pkg
+- /root/go/bin
+
+## xena/nim
+
+```ruby
+from "xena/nim:0.17.2"
+
+[
+    "project.nimble",
+    "public",
+    "src",
+].each { |x| copy x, "/app/" + x }
+
+run "cd /app && nimble update && yes | nimble build"
+
+cmd "sh -c 'cd /app && ./project'"
+
+# clean up
+run %q[ rm -rf /root/.nimble /opt ./src/nimcache && apk del libc-dev gcc curl libgcc git perl xz tar nim-compiler-deps ]
+
+flatten
+tag "user/project"
+```
+
+---
+
+[alpine-linux]: https://alpinelinux.org