Suggested improvements to Webhooks API documentation

Combining Python-style {<variable>} string substitution in JSON data easily lends itself to confusion, especially with cURL examples where it does not really make sense. Consider using some other notation such as Bash-style $<variable> or JavaScript-style ${<variable>} instead.
Create a subscription does not explicitly state that the POST method must be used. By default cURL will use POST even without specifying -X POST when the request contains data, but in other environments this could lead to confusion if GET is used instead, which results in a 400 response.
Update a subscription example's data contains malformed JSON. There is a comma missing between event_filters and enabled.
Validating received events is unclear. Consider providing a simple code example such as those below.
```
#!/usr/bin/env python3
```

import hmac

def validate_received_event(signature, secret, body): digest = hmac.new(secret.encode('utf-8'), body.encode('utf-8'), 'sha256').hexdigest() return hmac.compare_digest(signature, f'sha256={digest}')

```rb
#!/usr/bin/env ruby

require 'openssl'

def validate_received_event(signature, secret, body)
  signature == "sha256=#{OpenSSL::HMAC.hexdigest('SHA256', secret, body)}"
end

Also it would be nice if the issues related to implementing webhooks were closed, since they are among the top results on a web search and the excerpts mislead one to believe that it has not yet been released.

toggl / toggl_api_docs

Suggested improvements to Webhooks API documentation #438