[chore] fix broken buildx (whoops) (#1116)

CONTRIBUTING.md

@@ -338,16 +338,25 @@ If you prefer a simple approach to building a Docker container, with fewer depen
 
 The above command first builds the `gotosocial` binary, then invokes Docker buildx to build the container image.
 
+If you want to build a docker image for a different CPU architecture without setting up buildx (for example for ARMv7 aka 32-bit ARM), first modify the Dockerfile by adding the following lines to the top (but don't commit this!):
+
+```dockerfile
+# When using buildx, these variables will be set by the tool:
+# https://docs.docker.com/engine/reference/builder/#automatic-platform-args-in-the-global-scope
+# However, declaring them as global build arguments like this allows them to be set manually with `--build-arg` instead. 
+ARG BUILDPLATFORM
+ARG TARGETPLATFORM
+```
 
-If you want to build a docker image for a different CPU architechture without setting up buildx (for example for ARMv7 aka 32-bit ARM), you can use:
+Then, you can use the following command:
 
 ```bash
 GOOS=linux GOARCH=arm ./scripts/build.sh && docker build --build-arg BUILDPLATFORM=linux/amd64 --build-arg TARGETPLATFORM=linux/arm/v7 -t superseriousbusiness/gotosocial:latest .
 ```
 
 See also: [exhaustive list of GOOS and GOARCH values](https://gist.github.com/lizkes/975ab2d1b5f9d5fdee5d3fa665bcfde6)
-And: [exhaustive list of possible values for docker's `--platform`](https://github.com/tonistiigi/binfmt/#build-test-image)
 
+And: [exhaustive list of possible values for docker's `--platform`](https://github.com/tonistiigi/binfmt/#build-test-image)
 
 ## Financial Compensation
 

Dockerfile

@@ -1,12 +1,6 @@
 # syntax=docker/dockerfile:1.3
 # Dockerfile reference: https://docs.docker.com/engine/reference/builder/
 
-# When using buildx, these variables will be set by the tool:
-# https://docs.docker.com/engine/reference/builder/#automatic-platform-args-in-the-global-scope
-# However, declaring them as build arguments like this allows them to be set manually with `--build-arg` as well. 
-ARG BUILDPLATFORM
-ARG TARGETPLATFORM
-
 # stage 1: generate up-to-date swagger.yaml to put in the final container
 FROM --platform=${BUILDPLATFORM} quay.io/goswagger/swagger:v0.30.0 AS swagger