Add 3.8 alpine, update readme

Dockerfile

@@ -1,7 +1,7 @@
 #
 # Dockerfile for alpine-builder
 #
-FROM alpine:3.7
+FROM alpine:3.8
 LABEL maintainer "jar3b <hellotan@live.ru>"
 RUN apk add --no-cache alpine-sdk libressl-dev mariadb-dev postgresql-dev gdbm-dev readline-dev bash libtool autoconf \
     automake perl-dev python2-dev openldap-dev krb5-dev unixodbc-dev linux-pam-dev sqlite-dev talloc-dev libpcap-dev \

README.md

@@ -1,16 +1,20 @@
 # alpine-builder
 Docker image with alpine linux to build apk's
 
-Created user `builder` with with no password because `abuild -r` cannot be executed with root account.
+Created user `builder` with with no password because `abuild -r` cannot be executed on root account.
 
 
-### Usage:
+## Usage:
+
+### With external artifacts storage upload
+
 Here is illustration how to integrate this image with your CI/CD software,
 in this case i use GitLab CE + Sonatype Nexus as artifacts storage. Only one
 tricky thing is to create variable in GitLab CI with plain http auth to your
 Nexus server named `APK_REPO_CRED`.
 
-_.gitlab-ci.yml_
+`.gitlab-ci.yml`
+
 ```yaml
 image: jar3b/alpine-builder:3.7
 stages:
@@ -29,7 +33,27 @@ release:
     - curl -v -u ${APK_REPO_CRED} --upload-file myrepo-lib-$RV.apk $REPO/myrepo-lib-$RV.apk
 ```
 
-### Available versions:
+### With gitlab build artifacts
+ 
+Another option for gitlab-ci is using build artifacts like so:
+
+```yaml
+image: jar3b/alpine-builder:3.7
+stages:
+  - release
+
+release:
+  stage: release
+  variables:
+    RV: "1.0.1-r1"
+  script:
+    - abuild checksum
+    - abuild -r
+    - cd /home/builder/packages/${CI_PROJECT_NAMESPACE}/x86_64
+``` 
+
+## Available versions:
 - 3.5
 - 3.6
-- 3.7 (latest)
+- 3.7
+- 3.8 (latest)