Enhance the discoverability of the documentation for Weaver, Jinja, and Semantic Conventions

[lquerel]

As @marcalff mentioned in comment #227 (comment) , it would be beneficial to add the following comment into the jinja templates present in our examples and documentation.

{#
  Copyright The OpenTelemetry Authors
  SPDX-License-Identifier: Apache-2.0
  This file is:
  - a Jinja template,
  - used to generate semantic conventions,
  - using weaver.
  For doc on the template syntax:
  https://jinja.palletsprojects.com/en/3.0.x/
  For doc on the semantic conventions:
  https://github.com/open-telemetry/semantic-conventions
  For doc on weaver:
  https://github.com/open-telemetry/weaver
#}

[jsuereth]

As a thought - if someone wanted to investigate setting up https://rust-lang.github.io/mdBook/ that'd be amazing.