[Bug]: cargo package features are ill documented

[justinabrahms]

What happened?

I went to install opentelemetry_sdk and saw that there are several flags. I went to look into what they are and I couldn't find any relevant documentation that covered them.

I looked in the following locations:

• https://github.com/open-telemetry/opentelemetry-rust/tree/main/opentelemetry (readme)
• https://github.com/open-telemetry/opentelemetry-rust/blob/main/opentelemetry/Cargo.toml#L34
• https://github.com/open-telemetry/opentelemetry-rust/tree/main/opentelemetry-sdk (readme)
• https://github.com/open-telemetry/opentelemetry-rust/blob/main/opentelemetry-sdk/Cargo.toml#L46

API Version

0.21.0

SDK Version

0.21.2

What Exporters are you seeing the problem on?

N/A

Relevant log output

cargo add --package $MYTHING opentelemetry
    Updating crates.io index
      Adding opentelemetry v0.21.0 to dependencies.
             Features:
             + pin-project-lite
             + trace
             - logs
             - logs_level_enabled
             - metrics
             - testing

cargo add --package $MYTHING opentelemetry_sdk
    Updating crates.io index
      Adding opentelemetry_sdk v0.21.2 to dependencies.
             Features:
             + async-trait
             + crossbeam-channel
             + percent-encoding
             + rand
             + trace
             - async-std
             - glob
             - http
             - jaeger_remote_sampler
             - logs
             - logs_level_enabled
             - metrics
             - opentelemetry-http
             - rt-async-std
             - rt-tokio
             - rt-tokio-current-thread
             - serde
             - serde_json
             - testing
             - tokio
             - tokio-stream
             - url
    Updating crates.io index

[justinabrahms]

Noting that some of the things are documented here, but not all of them. https://github.com/open-telemetry/opentelemetry-rust/blob/main/opentelemetry-sdk/src/lib.rs#L80