Clarify description of With function

[tomwheeler]

I found the previous wording confusing, as the use of "prepend" suggests a position of the key-value pairs that was different than what I observed in the output.

What was changed

I reworded a comment that appears in the generated documentation.

Why?

The comment previously said, "With returns Logger instance that prepend every log entry with keyvals. If logger implements WithLogger it is used, otherwise every log call will be intercepted."

I interpret the use of "prepend" to mean that the key-value pairs I supply will appear first in the output. However, I found that they are the last things to appear. After further experimentation, I found that the KV pairs supplied to With appear after both the KV pairs in the parent logger and the string that I provided in the log statement, although they do appear before any KV pairs included in a specific log statement.

Chad Retz from the SDK team agreed that prepend was not the correct verb to use here, so I have reworded to remove it. As a result, it no longer makes any guarantee about the position of these key-value pairs, but that seemed like an implementation detail, and I find it to be more clear now because I'm no longer misguided about where within the output line I should be looking.

Checklist

1. Closes N/A

2. How was this tested:
   I ran go doc --all in the log subdirectory of my sdk-go clone and verified that the comment appeared as I had intended.

3. Any docs updates needed?

This change updates the only documentation about log.With of which I am aware.

[cretz]

The CI failure is due to bad cloud secret. I am looking into updating now.