logs-logs-logs: tweak introduction

[ErikSchierboom]

The introduction.md document of the logs-logs-logs exercise could use some tweaks.

Runes are in backticks leading the student to believe it is an actual type, but the type is rune. The runes word should not be in backticks, or if it refers to the rune type, be replaced with rune[].

When possible, the introduction should not contain links (especially not to "deep dives"), so the following section should be removed:

Strings, bytes, runes and characters in Go provides a deep dive into this topic.