Clarify span status guidance for HTTP spans

[arminru]

It was not clear if "status message" refers to the general span status description or the HTTP reason phrase (see Gitter request).

[bogdandrutu]

@arminru please try to follow the rules for contributing referenced here https://github.com/open-telemetry/opentelemetry-specification/blob/master/CONTRIBUTING.md#contributing and written here https://github.com/open-telemetry/community/blob/master/CONTRIBUTING.md#github-workflow :) Don't need to do anything now but for the future.

[arminru]

@bogdandrutu Sorry about that, I used the Edit✏️ feature right from the Github website which only allows me to commit on a branch since I have write access to the repo, otherwise it would've used my own fork. I thought it wouldn't matter since that's a change that I expected to merge rather instantly anyway. I'll use the more cumbersome manual approach on my local machine in future then to avoid this. 🙂

[Oberon00]

@bogdandrutu You should make a PR to add this caveat to CONTRIBUTING.md for people with write-access to take care of. I suspect there will be push-back however 😉

[bogdandrutu]

@Oberon00 I added the links there is already in the contributing reference to that

[carlosalberto]

Merged - this was a relatively minor clarification and had two approvals already (but had been standing forgotten for some time now ;( )