Fix manual devcontainer workflow on Linux

This ensures that devcontainer can be built and manually run based on
the README.md instructions

Signed-off-by: eriknordmark <erik@zededa.com>

.devcontainer/Dockerfile

@@ -1,7 +1,7 @@
 # syntax=docker/dockerfile:1.6.0
 FROM alpine:3.18
 
-ARG TARGETOS
+ARG TARGETOS=linux
 ARG TARGETARCH
 ARG PROTOC_GEN_GO_VERSION=1.31.0
 ARG PROTOC_VERSION=23.4
@@ -17,7 +17,7 @@ RUN arch=$(uname -m); \
   unzip protobuf.zip -d /usr/local; \
   rm -f protobuf.zip
 
-ADD https://github.com/seamia/protodot.git /protodot
+RUN git clone https://github.com/seamia/protodot.git /protodot
 RUN go build -C /protodot -o /usr/local/bin/protodot .
 
 RUN mkdir -p $(go env GOPATH)

README.md

@@ -103,6 +103,14 @@ devcontainer --workspace-folder . up
 devcontainer exec --workspace-folder . make proto
 ```
 
+#### Manual ad-hoc use of devcontainer on Linux
+
+First the devcontainer needs to be built and then run to do the make proto:
+```bash
+docker build -f .devcontainer/Dockerfile -t eve-api-builder .
+docker run --rm -v $(pwd):/src -w /src -u $(id -u) eve-api-builder make proto
+```
+
 #### Local
 
 If running locally, you need to install the prerequisites yourself.