devcontainer: add doc, user to match host machine, and scripts to build/start

ops/devcontainer/Dockerfile

@@ -2,7 +2,20 @@
 
 FROM alpine:3.22
 
-RUN apk add build-base git go sqlite shellcheck curl jq bash docker
+RUN apk add build-base git go sqlite shellcheck curl jq sudo bash docker
+
+# Busybox `less` doesn't appear to support colors (makes git diff lose color)
+RUN apk add less
 
 RUN curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b /usr/local/bin v2.0.2
 RUN GOBIN=/usr/local/bin go install git.offline-twitter.com/offline-labs/gocheckout@v0.0.2
+
+# Create a user in the container with the same UID as on the host machine, to avoid ownership conflicts.
+# The user gets sudo of course.
+ARG USERNAME
+ARG UID
+ARG GID
+RUN addgroup -g ${GID} ${USERNAME}
+RUN adduser -D -u ${UID} -G ${USERNAME} ${USERNAME}
+RUN echo "${USERNAME} ALL=(ALL) NOPASSWD:ALL" > /etc/sudoers.d/${USERNAME}
+USER ${USERNAME}