[Docs] OpenWrt Feeds Configuration

[eallion]

As the official documentation suggests, The git method can specify a specific branch or commit using the following formats:

• https://openwrt.org/docs/guide-developer/feeds

src-git local_feed_name https://example.com/repo_name/something.git;branch_name
src-git local_feed_name https://example.com/repo_name/something.git^commit_hash

feeds.conf.default:

src-git helloworld https://github.com/fw876/helloworld.git;main