Cleaning up examples/ models and starter .env files (#1124)

Closes https://github.com/go-skynet/LocalAI/issues/1066 and
https://github.com/go-skynet/LocalAI/issues/1065

Standardizes all `examples/`:
- Models in one place (other than `rwkv`, which was one-offy)
- Env files as `.env.example` with `cp`
    - Also standardizes comments and links docs

examples/langchain-huggingface/models

@@ -0,0 +1 @@
+../models

examples/langchain-huggingface/models/completion.tmpl

@@ -1 +0,0 @@
-{{.Input}}

examples/langchain-huggingface/models/gpt-3.5-turbo.yaml

@@ -1,17 +0,0 @@
-name: gpt-3.5-turbo
-parameters:
-  model: gpt2
-  top_k: 80
-  temperature: 0.2
-  top_p: 0.7
-context_size: 1024
-backend: "langchain-huggingface"
-stopwords:
-- "HUMAN:"
-- "GPT:"
-roles:
-  user: " "
-  system: " "
-template:
-  completion: completion
-  chat: gpt4all

examples/langchain-huggingface/models/gpt4all.tmpl

@@ -1,4 +0,0 @@
-The prompt below is a question to answer, a task to complete, or a conversation to respond to; decide which and write an appropriate response.
-### Prompt:
-{{.Input}}
-### Response: