Clarify guidelines

[rayegun]

Clarify that according to the General README these are guidelines not rules, and as such may be overridden with sufficient justification.

[rayegun]

I believe this was changed at some point from guidelines to rules, given that there are broken links on General/README.md.

I am strongly in favor of maintaining the word guidelines, not the word rules. Names are by nature a deeply personal part of the package development process. With sufficient justification and/or rebuttals to community name feedback we should feel comfortable merging package author preferred names.

In addition it must be clear that renaming suggestions are suggestions. Users who point to Pkg.jl docs as "rules" rather than guidelines are empowered to outright deny names, rather than offer constructive suggestions. I receive frequent complaints about weaponization of the rules/guidelines from new and existing community members.

Explicitly stating that these are guidelines provides more support for package authors who feel they are being demanded to make changes rather than being suggested.