First stab at a modelfile doc

Signed-off-by: Matt Williams <m@technovangelist.com>

docs/modelfile.md

+# Ollama Model File Reference
+
+Ollama can build models automatically by reading the instructions from a Modelfile. A Modelfile is a text document that represents the complete configuration of the Model. You can see that a Modelfile is very similar to a Dockerfile.
+
+## Format
+
+Here is the format of the Modelfile:
+
+```modelfile
+# comment
+INSTRUCTION arguments
+```
+
+Nothing in the file is case-sensitive. However, the convention is for instructions to be uppercase to make it easier to distinguish from the arguments.
+
+A Modelfile can include instructions in any order. But the convention is to start the Modelfile with the FROM instruction.
+
+Although the example above shows a comment starting with a hash character, any instruction that is not recognized is seen as a comment. 
+
+## FROM
+
+```modelfile
+FROM <image>[:<tag>]
+```
+
+This defines the base model to be used. An image can be a known image on the Ollama Hub, or a fully-qualified path to a model file on your system
+
+## PARAMETER
+
+The PARAMETER instruction defines a parameter that can be set when the model is run. 
+
+```modelfile
+PARAMETER <parameter> <parametervalue>
+```
+
+### Valid Parameters and Values
+
+| Parameter        | Description                                                                                 | Value Type | Value Range |
+| ---------------- | ------------------------------------------------------------------------------------------- | ---------- | ----------- |
+| NumCtx           |                                                                                             | int        |             |
+| NumGPU           |                                                                                             | int        |             |
+| MainGPU          |                                                                                             | int        |             |
+| LowVRAM          |                                                                                             | bool       |             |
+| F16KV            |                                                                                             | bool       |             |
+| LogitsAll        |                                                                                             | bool       |             |
+| VocabOnly        |                                                                                             | bool       |             |
+| UseMMap          |                                                                                             | bool       |             |
+| EmbeddingOnly    |                                                                                             | bool       |             |
+| RepeatLastN      |                                                                                             | int        |             |
+| RepeatPenalty    |                                                                                             | float      |             |
+| FrequencyPenalty |                                                                                             | float      |             |
+| PresencePenalty  |                                                                                             | float      |             |
+| temperature      | The temperature of the model. Higher temperatures result in more creativity in the response | float      | 0 - 1       |
+| TopK             |                                                                                             | int        |             |
+| TopP             |                                                                                             | float      |             |
+| TFSZ             |                                                                                             | float      |             |
+| TypicalP         |                                                                                             | float      |             |
+| Mirostat         |                                                                                             | int        |             |
+| MirostatTau      |                                                                                             | float      |             |
+| MirostatEta      |                                                                                             | float      |             |
+| NumThread        |                                                                                             | int |             |
+
+
+## PROMPT
+
+Prompt is a multiline instruction that defines the prompt to be used when the model is run. Typically there are 3-4 components to a prompt: System, context, user, and response.
+
+```modelfile
+PROMPT """
+{{- if not .Context }}
+### System:
+You are a content marketer who needs to come up with a short but succinct tweet. Make sure to include the appropriate hashtags and links. Sometimes when appropriate, describe a meme that can be includes as well. All answers should be in the form of a tweet which has a max size of 280 characters. Every instruction will be the topic to create a tweet about.
+{{- end }}
+### Instruction:
+{{ .Prompt }}
+
+### Response:
+"""
+
+```
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