fix build instructions

[newca12]

fix #52
If you want to lean more about this issue check : https://stackoverflow.com/a/1032653

From git version 1.8.3 to the latest version.
git submodule update --init --recursive will not check out the uptodate submodule.
--remote is required

Building without --remote fetch the old Rust.stg template and the visitor feature introduce in V0.3 will not work.
Nevetheless the released V0.3.0 asset antlr4-4.8-2-SNAPSHOT-complete.jar is OK which is a bit surprising.

[rrevenantt]

Thanks, i am not sure why you find it surprising tho, release assets are built and uploaded directly from CI which fetches target commit directly.

[newca12]

The CI use /usr/bin/git -c protocol.version=2 submodule update --init --force --depth=1
so the wrong old submodule version is checkout
Submodule path 'runtime/Rust': checked out '76d0a7dde296bb194242a1430d88fdd6b79ac2eb'

but the released artifact is indeed correct thanks to the next github action

      - run: |
          git fetch origin $GITHUB_REF
          git checkout FETCH_HEAD

which ensure the right module refresh HEAD is now at 4779134 v0.3 prerelease (#29)

This is not that obvious but if you know what you are doing this is fine as the Checkout Submodule Action which was doing this properly is not maintened anymore.