[chore] [receiver/collectd] Fix README copy-paste (open-telemetry#43857)

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#### Description
The description for the `timeout` config field was inacurrate, and
appears to have been copied from [the dockerstats receiver
docs](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/9b02d0acb7a4657a7f136c1334471ea25c2043ae/receiver/dockerstatsreceiver/README.md?plain=1#L44)
:)

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#### Link to tracking issue
I didn't make one. I can, this just seems pretty trivial.

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#### Testing

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#### Documentation

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Author: braydonk

receiver/collectdreceiver/README.md

@@ -37,7 +37,7 @@ The following settings are required:
 The following settings are optional:
 
 - `attributes_prefix` (no default): Used to add query parameters in key=value format to all metrics.
-- `timeout` (default = `30s`): The request timeout for any docker daemon query.
+- `timeout` (default = `30s`): Used as the `read_timeout` and `write_timeout` for the listening server.
 
 Example: