Add documentation to README

Author: wallento

README.md

@@ -1,2 +1,110 @@
-EDA Container Wrapper
-=====================
+# EDA Container Wrapper
+
+EDA container wrapper is a work-in-progress generic wrapper tool around open
+source EDA tools. The tools are executed in Docker containers and this tool
+wraps this execution and keeps an inventory of tools.
+
+It supports three use cases:
+
+1. Run `eda-container-wrapper` to execute the wrapper with given parameters
+2. Let `eda-container-wrapper` create a wrapper script (in an executable path for example) with pre-defined settings
+3. Run tools from python using the `edacontainerwrapper` module
+
+The settings can be set in the following way in precedence order:
+
+1. As parameters to the `eda-container-wrapper` tool or to the respective functions of `edacontainerwrapper`
+2. As environment variables
+3. As default settings in the wrapper scripts
+
+## Installation
+
+```shell
+$ pip3 install eda-container-wrapper
+```
+
+## Supported settings
+
+### Tool version (`--tool-version` or `ECW_TOOL_VERSION`, default: depends on tool)
+
+Sets the version of the tool to use.
+
+### Interactive (`--non-interactive` or `ÈCW_INTERACTIVE`, default: interactive)
+
+Runs the Docker container in interactive mode (allowing to terminate it easily
+for example) with the Docker `-ti` flags. Some non-interactive environments such
+as CI don't support that (missing tty). Note the difference in logic, the
+default is interactive mode which is disabled with the `--non-interactive`
+switch. `ECW_INTERACTIVE` keeps it interactive when set to `true` or `1` and it
+will be non-interactive otherwise.
+
+### Current work directory base (`--cwd-base` or `ECW_CWD_BASE`, default: not set)
+
+If not empty this is a colon-separated pair of a leading path of the cwd where
+the tool was called from and a replacement for this path. This is in particular
+useful when called from inside a Docker container, such as in CI. The syntax is:
+`<actual path>:<cwd path>`.
+
+### Split the current working directory (`--split-cwd-tail` or `ECW_SPLIT_CWD_TAIL`, default: `0`)
+
+When mapping the current working directory, this setting actually maps the path
+up the hierarchy by the given value. This is in particular useful when you need
+to access data relative to the current working directory that is in upper and
+sibbling folders.
+
+For example, when started from the following folder:
+
+```
+CWD=/path/to/my/project/build
+```
+
+Setting `--split-cwd-tail=1` the split is into `/path/to/my/project` and
+`build`. Each tool has a "project path" that is the volume where the tool is
+executed in then by setting the working directory. For a tool with the project
+path `/project` it will then mount `/path/to/my/project` to `/project` and the
+workdir will be `/project/build`.
+
+This split is executed after processing the `cwd base`.
+
+## Running a Tool
+
+As described above there are different ways to run a tool, that are described in
+the following.
+
+### Run `eda-container-wrapper`
+
+The program is called with the parameters as described and the toolname.
+Following a `--` parameters to the tool can be supplied.
+
+Example:
+
+```shell
+$ eda-container-wrapper verilator -- --version
+```
+
+### Create wrapper
+
+To create a `verilator` script that by default executes version 4.100:
+
+```shell
+$ eda-container-wrapper --write-script=/usr/local/bin/verilator --tool-version 4.100 verilator
+```
+
+and then execute it:
+
+```shell
+$ verilator --version
+Verilator 4.100 2020-09-07 rev v4.100
+```
+
+Setting the environment setting `ECW_TOOL_VERSION` changes the defualt behavior:
+
+```shell
+$ ECW_TOOL_VERSION=4.102 verilator --version
+Verilator 4.102 2020-10-15 rev v4.102
+```
+
+It can be useful to create the script in your virtual environment:
+
+```shell
+$ eda-container-wrapper --write-script=$VIRTUAL_ENV/verilator --tool-version 4.100 verilator
+```