guide: add "Best Practices"

[efiop]

UPDATE: Possibly as a How To guide (see #899)

Looks like we need a special section describing ways how to organize your projects:

• how to use DVC with DB (see how to use DVC when the data is stored in a DB #594)
• our default Dvcfile trick
• manually editing dvc.yaml + dvc commit or dvc repro (see also how to: "update your pipeline by editing DVC-files" #230 (comment))
  it's safe to edit DVC files, no need to touch or update md5, DVC will take care of it
  UPDATE: See dvc.yaml: encourage manual writing/editing stages (and pipelines) #2578
• specify meaningful stage names with -f
• creating a pipeline in a 'debug' directory and then moving it to different data sets
• creating a pipeline in a 'debug' directory and then modifying respective DVC files to set different data sets as an input
• add "use meta to preserve your content" - describe "meta" field in stage file and that we are preserving comments #306
• never store user credentials in the DVC project config
• one vs many dvc.yaml files (from pipelines: clarify whether it's possible to have more than one _pipeline file_ for a DVC project in the docs #2170 (comment))

See also the latest relevant #72 (comment) and below.

[efiop]

Also worth mentioning our default Dvcfile trick.

[shcheklein]

it's safe to edit dvc files, no need to touch or update md5, dvc will take care of it

[shcheklein]

Specify meaningful stage names

[shcheklein]

Also, we are not sure about branches anymore.

[shcheklein]

Never store user credentials in the DVC project config.

[dmpetrov]

@shcheklein we should keep branches - it is a good practice. However, we should mention that for some cases like hyperparameters tuning branches are not very relevant.

[shcheklein]

@dmpetrov agreed, you are right. I just probably wanted to highlight that we should not be pushing branches as a single best option in all case - there are tags, directories, may be even mention other tools for now?

[dmpetrov]

@shcheklein also we need to implement experiment dir\output feature for hyperparameters tuning use case (Stefan's use case).

[shcheklein]

add "use meta to preserve your content" - #306