Add riscv64 support to docker builds

* Adjust GitHub CI to also build for riscv64
* Update base Ubuntu base for build from 18.04 LTS to 20.04 LTS as to support riscv64
* Minor: Exclude idea IDE files from git

.github/workflows/build.yaml

@@ -16,7 +16,7 @@ on:
 env:
   DOCKER_REPO: shenxn/protonmail-bridge
   DOCKER_REPO_DEV: ghcr.io/shenxn/protonmail-bridge-dev
-  PLATFORMS: linux/amd64,linux/arm64/v8,linux/arm/v7
+  PLATFORMS: linux/amd64,linux/arm64/v8,linux/arm/v7,linux/riscv64
 
 jobs:
   build:

.gitignore

@@ -1 +1,3 @@
+# Ignoring IDE-specific files
+.idea/*
 .vscode

README.md

@@ -20,7 +20,7 @@ We now support ARM devices (`arm64` and `arm/v7`)! Use the images tagged with `b
 
 There are two types of images.
  - `deb`: Images based on the official [.deb release](https://protonmail.com/bridge/install). It only supports the `amd64` architecture.
- - `build`: Images based on the [source code](https://github.com/ProtonMail/proton-bridge). It supports `amd64`, `arm64`, and `arm/v7`. Supporting to more architectures is possible. PRs are welcome.
+ - `build`: Images based on the [source code](https://github.com/ProtonMail/proton-bridge). It supports `amd64`, `arm64`, `arm/v7` and `riscv64`. Supporting to more architectures is possible. PRs are welcome.
 
 tag | description
  -- | --

build/Dockerfile

@@ -9,7 +9,7 @@ WORKDIR /build/
 COPY build.sh VERSION /build/
 RUN bash build.sh
 
-FROM ubuntu:bionic
+FROM ubuntu:focal
 LABEL maintainer="Xiaonan Shen <s@sxn.dev>"
 
 EXPOSE 25/tcp