docs: build custom-plugin in docker not working

[Vacant2333]

What happened:
run this command for build the example custom-plugin:

docker run -v `pwd`:/work golang:1.14-alpine sh -c "cd /work && apk add musl-dev gcc && go build -buildmode=plugin magic.go"

will cause:

and i find out that we have the go.mod file before:
https://github.com/volcano-sh/volcano/pull/1218/files#diff-98b4a278f2b96122392377740a91e7d348ecbf1323e06be2265c3e3ecf4f09bb

but we remove the go.mod at this pr:
#1988

im not sure how to resoulve this problem, i have try update the command like:

docker run -v `pwd`:/work golang:1.20-alpine sh -c "cd /work && apk add musl-dev gcc git && go mod init custom-plugin && go mod tidy && go build -buildmode=plugin magic.go"

but it will cause:

or maybe we can run this command at /volcano, just like:

docker run -v `pwd`:/volcano golang:1.20.1-alpine sh -c "cd /volcano/example/custom-plugin && apk add musl-dev gcc && go mod tidy && go build -buildmode=plugin magic.go"

i didnt find a good way to resoulve this problem, can u tell me a good way to fix it, and im happy to raise a pr to fix it!

What you expected to happen:
Build custom-plugin in docker

How to reproduce it (as minimally and precisely as possible):

cd example/custom-plugin
docker run -v `pwd`:/work golang:1.20-alpine sh -c "cd /work && apk add musl-dev gcc git && go mod download && go build -buildmode=plugin magic.go"

Environment:

• Volcano Version: latest
• Kubernetes version (use kubectl version):
• Cloud provider or hardware configuration:
• OS (e.g. from /etc/os-release): MacOS
• Kernel (e.g. uname -a):
• Install tools:
• Others:

[Monokaix]

I think docker build command should change to something like docker run -v pwd:/work golang:1.20-alpine sh -c "cd /work && apk add musl-dev gcc && go build -buildmode=plugin example/custom-plugin/magic.go and we should also change readme file to let user run a complete example.

[Vacant2333]

I think docker build command should change to something like docker run -v pwd:/work golang:1.20-alpine sh -c "cd /work && apk add musl-dev gcc && go build -buildmode=plugin example/custom-plugin/magic.go and we should also change readme file to let user run a complete example.

agree! i will raise a pr to fix it

[Monokaix]

/good-first-issue

[volcano-sh-bot]

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[Vacant2333]

/assign