update README.md

.gitignore

@@ -1,2 +1,3 @@
 # Created by .ignore support plugin (hsz.mobi)
-.idea
+.idea
+drone-upx

Dockerfile

@@ -1,8 +1,9 @@
 FROM alpine
 
-ADD drone-upx /bin/
-ADD upx /bin/
+ADD https://github.com/upx/upx/releases/download/v3.95/upx-3.95-amd64_linux.tar.xz /usr/local
+RUN xz -d -c /usr/local/upx-3.95-amd64_linux.tar.xz | tar -xOf - upx-3.95-amd64_linux/upx > /bin/upx && \
+    chmod a+x /bin/upx
 
-#RUN apk -Uuv add ca-certificates
+ADD drone-upx /bin/
 
 ENTRYPOINT /bin/drone-upx