Add package readme howto guide

[mrodm]

This PR adds a how to guide for developers to have documentation to write the required README.md files.

A link to this documentation has been added in the elastic-package build command description.

Closes #349

[elasticmachine]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Start Time: 2022-08-22T11:56:20.658+0000

• Duration: 28 min 1 sec

Test stats 🧪

Test	Results
Failed	0
Passed	778
Skipped	0
Total	778

🤖 GitHub comments

To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

[elasticmachine]

🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (32/32)	💚
Files	66.949% (79/118)	👍
Classes	62.424% (103/165)	👍
Methods	49.55% (330/666)	👍
Lines	33.136% (2963/8942)	👍
Conditionals	100.0% (0/0)	💚

[mtojek]

LGTM!

[bmorelli25]

@colleenmcginnis added detailed documentation guidelines for integration readme files in elastic/integrations#3433. Does it make more sense to move that content to this new file? Where can these docs be seen by the greatest number of people?

[mrodm]

@bmorelli25 thanks for pointing out that doc in integrations. Looking at both PRs, I would see that they are both complementary to each other.

According to what I see, on the one hand, the PR in integrations repository by @colleenmcginnis (elastic/integrations#3433) are guidelines to follow in that repository to create new readme files, and I would say it could be kept in that repository.

On the other hand, this PR is specifically about what syntax and features are allowed by elastic-package build command to be used when writing those readme templates.

Would it make sense to keep both as they are and add a link from https://github.com/elastic/integrations/blob/main/docs/documentation_guidelines.md to this file https://github.com/elastic/elastic-package/blob/main/docs/howto/add_package_readme.md ? Thereby, developers would be able to check what they can use in those readme templates from the guidelines. WDYT ?

Feel free to chime in @ecosystem

[bmorelli25]

Gotcha. This PR is about elastic-package build. And I'm thinking about the documentation template more in the context of elastic-package create package.

I think the best solution is to integrate the doc template into elastic-package create package—which Colleen will be attempting as a part of #880.

Meanwhile, as you suggested above, cross linking between the add_package_readme.md and documentation_guidelines.md also probably makes sense.