Update backward compatibility promise in CONTRIBUTING.md to reflect HIP 0004 about helm HOT 3 CLOSED

@banjoh thanks for making this follow-up issue! Adding my replies from slack here for better transparency.

Should this also include changing functionality?

HIP-0004 covers that point, indirectly, by linking to another article that covers it:

exported Go APIs will remain compatible as per this article

that article, under “Add configuration methods”, says:

So far we’ve talked about overt breaking changes, where changing a type or a function would cause users’ code to stop compiling. However, behavior changes can also break users, even if user code continues to compile…

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how about changing this:

We also try very hard to not change publicly accessible Go library definitions inside of the pkg/ directory of our source code.
to something like:

We also remain committed to not change publicly accessible Go library definitions inside of the pkg/ directory of our source code in a non-backwards-compatible way.

and link to the HIP like you suggested, for more details on Helm’s minor and patch release backwards-compatibility rules before the summary bulletin list?

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I'll incorporate your suggestions in a PR.

Leaving the description as is, else comments won't make sense afterwards :)

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