Add doc/standalone.md

Author: chubin

doc/standalone.md

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+
+You don't need to install anything, to start using *cheat.sh*.
+The only tool that you need is *curl*, which is typically installed
+in every system. In the rare cases when *curl* is not installed,
+there should be one of its alternatives in the system: *wget*, *wget2*,
+*httpie*, *ftp* (with HTTP support), *fetch*, etc.
+
+There are two cases, when you want to install *cheat.sh* locally:
+
+1. You plan to use it off-line, without Internet access;
+2. You want to use your own cheat sheets (additionally, or as a replacement).
+
+In this case you need to install cheat.sh locally.
+
+## How to install cheat.sh locally
+
+To use cheat.sh offline, you need to:
+
+1. Install it,
+2. Fetch its data sources.
+
+If you already have the cht.sh cli client locally,
+you can use it for the standalone installation.
+Otherwise it must be installed first.
+
+```
+    curl https://cht.sh/:cht.sh > ~/bin/cht.sh
+    chmod +x ~/bin/cht.sh
+```
+
+Now you can install cheat.sh locally:
+
+```
+    cht.sh --standalone-install
+```
+
+During the installation process, cheat.sh and its
+data sources will be installed locally.
+
+By default `~/.cheat.sh` is used as the installation
+directory.
+
+![cheat.sh standalone installation](https://user-images.githubusercontent.com/3875145/57986904-ef3f1b80-7a7a-11e9-9531-ef37ec74b03a.png)
+
+## Update cheat sheets
+
+Cheat sheets are fetched and installed to `~/.cheat.sh/upstream`.
+To keep the cheat sheets up to date,
+run the `cheat.sh` `update-all` command on regular basis.
+Ideally, add it to *cron*:
+
+```
+0 5 0 0 0 $HOME/.cheat.sh/ve/bin/python $HOME/.cheat.sh/lib/fetch.py update-all
+```
+
+In this example, all information sources will be updated
+each day at 5:00 local time, on regular basis.
+
+## cheat.sh server mode
+
+Your local cheat.sh installation is full-fledged, and it can
+handle incoming HTTP/HTTPS queries.
+
+To start cheat.sh in the server mode, run:
+
+```
+$HOME/.cheat.sh/ve/bin/python $HOME/.cheat.sh/bin/srv.py
+```
+
+You can also use `gunicorn` to start the cheat.sh server.
+
+
+## Docker
+
+You can deploy cheat.sh as a docker container.
+Use `Dockerfile` in the source root directory, to build the Docker image:
+
+```
+docker build .
+```
+
+## Limitations
+
+Some cheat sheets not available in the offline mode
+for the moment. The reason for that is that to process some queries,
+cheat.sh needs to access the Internet itself, because it does not have
+the necessary data locally. We are working on that how to overcome
+this limitation, but for the moment it still exists.
+