Update 'README.md'

README.md

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 # docker-rusty-moon
 
+Docker image intended for Rust apps cross-compilation.  
+Based on [ubuntu:latest](https://hub.docker.com/_/ubuntu) (latest LTS official image), it provides latest **nightly** Rust with the following targets:
+- x86_64-unknown-linux-gnu
+- x86_64-pc-windows-gnu
+
+## Build 
+To build image locally:  
+`docker build https://inex.dev/lnkr/docker-rusty-moon.git -t lnkr/rust:latest`
+
+Image is available at [drone.lnkr.dev](https://drone.lnkr.dev/) drone.io instance as `lnkr/rust:latest` and rebuilds on a daily basis.
+
+## Usage
+Use this while defining steps:
+```
+image: lnkr/rust
+pull: never
+```
+### .drone.yml example
+```
+kind: pipeline
+name: default
+type: docker
+steps:
+- name: build & test
+  image: lnkr/rust
+  pull: never
+  commands:
+  - cargo build --target x86_64-unknown-linux-gnu
+  - cargo build --target x86_64-pc-windows-gnu
+  - cargo test
+```