splitting README.md into files in /docs for better readability

Signed-off-by: Claudius <opensource@amenthes.de>

docs/setup/cloudron.md

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+## Cloudron
+
+Install CodiMD on [Cloudron](https://cloudron.io):
+
+[![Install](https://cloudron.io/img/button.svg)](https://cloudron.io/button.html?app=io.hackmd.cloudronapp)

docs/setup/docker.md

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+
+## CodiMD by docker container
+[![Try in PWD](https://cdn.rawgit.com/play-with-docker/stacks/cff22438/assets/images/button.png)](http://play-with-docker.com?stack=https://github.com/codimd/container/raw/master/docker-compose.yml&stack_name=codimd)
+
+
+**Debian-based version:**
+
+[![Docker Repository on Quay](https://quay.io/repository/codimd/server/status "Docker Repository on Quay")](https://quay.io/repository/codimd/server)
+
+
+**Alpine-based version:**
+
+[![Docker Repository on Quay](https://quay.io/repository/codimd/server/status "Docker Repository on Quay")](https://quay.io/repository/codimd/server)
+
+The easiest way to setup CodiMD using docker are using the following three commands:
+
+```console
+git clone https://github.com/codimd/container.git
+cd codimd-container
+docker-compose up
+```
+Read more about it in the [container repository…](https://github.com/codimd/container)

docs/setup/heroku.md

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+## Heroku Deployment
+
+You can quickly setup a sample Heroku CodiMD application by clicking the button
+below.
+
+[![Deploy on Heroku](https://www.herokucdn.com/deploy/button.svg)](https://heroku.com/deploy?template=https://github.com/codimd/server/tree/master)

docs/setup/kubernetes.md

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+## Kubernetes
+
+To install use `helm install stable/hackmd`.
+
+For all further details, please check out the offical CodiMD  [K8s helm chart](https://github.com/kubernetes/charts/tree/master/stable/hackmd).

docs/setup/manual-setup.md

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+# Manual Installation
+
+## Requirements on your server
+
+- Node.js 6.x or up (test up to 7.5.0) and <10.x
+- Database (PostgreSQL, MySQL, MariaDB, SQLite, MSSQL) use charset `utf8`
+- npm (and its dependencies, [node-gyp](https://github.com/nodejs/node-gyp#installation))
+- `libssl-dev` for building scrypt (see [here](https://github.com/ml1nk/node-scrypt/blob/master/README.md#installation-instructions) for further information)
+- For **building** CodiMD we recommend to use a machine with at least **2GB** RAM
+
+## Instructions
+
+1. Download a release and unzip or clone into a directory
+2. Enter the directory and type `bin/setup`, which will install npm dependencies and create configs. The setup script is written in Bash, you would need bash as a prerequisite.
+3. Setup the configs, see more below
+4. Setup environment variables which will overwrite the configs
+5. Build front-end bundle by `npm run build` (use `npm run dev` if you are in development)
+6. Modify the file named `.sequelizerc`, change the value of the variable `url` with your db connection string
+   For example: `postgres://username:password@localhost:5432/codimd`
+7. Run `node_modules/.bin/sequelize db:migrate`, this step will migrate your db to the latest schema
+8. Run the server as you like (node, forever, pm2)
+
+
+## How to upgrade your installation
+
+:warning: When you are still running from the old repository, please run: `git remote set-url origin https://github.com/codimd/server.git` :warning:
+
+If you are upgrading CodiMD from an older version, follow these steps:
+
+1. Fully stop your old server first (important)
+2. `git pull` or do whatever that updates the files
+3. `npm install` to update dependencies
+4. Build front-end bundle by `npm run build` (use `npm run dev` if you are in development)
+5. Modify the file named `.sequelizerc`, change the value of the variable `url` with your db connection string
+   For example: `postgres://username:password@localhost:5432/codimd`
+6. Run `node_modules/.bin/sequelize db:migrate`, this step will migrate your db to the latest schema
+7. Start your whole new server!