Introduce documentation for each backend implementation

[riccardomc]

We need a consistent way to specify instructions and parameters documentation for each type of backend. We could restructure the secrets directory to contain a sub-directory for each backend with a README.md in it For example:

pkg/secrets/
  asm/
     asm.go
     asm_test.go
     README.md
  onepassword/
     onepassword.go
     onepassword_test.go
     README.md
...

And the README.md would look like something like:

AWS Secrets Manager Backend

Format

Type: "asm"
Name: "asm-example"
Parameters:
    accessKeyID: ""
    region: ""
    secretAccessKey: ""

Parameters

Parameter	Description	Required	Default
accessKeyID	AWS Access Key ID that can talk to AWS Secrets Manager	yes	""
region	AWS Region	yes	""
secretAccessKey	AWS Secret Access Key corresponding to accessKeyID	yes	""

[riccardomc]

@frankscholten @zemanel what do you think?

[zemanel]

docs is good! but for such a small proj, my vote is on everything on a single README (easier to search) ?

[riccardomc]

ok, I had that doubt as well... let's just use a "Supported Backends" in the main README.md then!

[frankscholten]

Yes. We can use a Markdown table and add a line for each backend with parameters.

[frankscholten]

#40