Updated readme.

README.md

@@ -4,12 +4,9 @@ Quickly run a WSL/Linux command from a Windows (e.g., PowerShell or CMD) prompt.
 [![ko-fi](https://www.ko-fi.com/img/githubbutton_sm.svg)](https://ko-fi.com/I3I1VA18)
 
 ## Introduction
-This is essentially a variant of [RunInBash](https://github.com/neosmart/RunInBash) designed to run Linux commands under WSL
-inside the bottle created by _genie_ (see https://github.com/arkane-systems/genie) if you aren't familiar with
-genie, which permits the use of _systemd_ and its services under WSL.
+This is essentially a variant of [RunInBash](https://github.com/neosmart/RunInBash) designed to run Linux commands under WSL inside the bottle created by _genie_ (see https://github.com/arkane-systems/genie) if you aren't familiar with genie, which permits the use of _systemd_ and its services under WSL.
 
-RunInGenie runs the supplied command using _genie -c_, feeding back stdout and stderr, and passing the return
-code back to the caller, for your convenience in building hybrid Windows/Linux scripts.
+RunInGenie runs the supplied command using _genie -c_, feeding back stdout and stderr, and passing the return code back to the caller, for your convenience in building hybrid Windows/Linux scripts.
 
 Simply prefix the Linux command with the dollar sign ($):
 
@@ -29,26 +26,63 @@ Note that by default pipes (|), etc., will be interpreted by PowerShell, so:
 $ ls -la 'C:\Program Files' | clip
 ```
 
-Will send the directory listing to the _Windows_ clip.exe. If you wish to pipe within WSL, you must escape it
-with a backtick (`), thus:
+Will send the directory listing to the _Windows_ clip.exe. If you wish to pipe within WSL, you must escape it with a backtick (`), thus:
 
 ```
 $ ls -la 'C:\Program Files' `| less
 ```
 
-## Installation
+### Shell
 
-Grab the latest RunInGenie.zip from the Releases page, unzip it, and put the resulting $.exe somewhere on your PATH. Easy!
+Using RunInGenie without specifying a command:
+
+```
+$
+```
+
+Opens a shell in the current directory, useful for entering multiple commands in sequence without returning to Windows.
+
+Please note that this _is not_ a login shell, and as such, for example, does not execute your login profile; `$` should not be used as a substitute for `wsl genie -s` to start a dedicated WSL shell. It's intended as a convenience for "I need a quick shell here" situations.
+
+### Distro selection
+
+Normally, RunInGenie executes Linux commands in the default WSL distribution (but see _Configuration_, below). This can be overriden by using the -d/--distro option, which must be the first thing specified after the `$`, and takes the distro name as shown by `wsl -l`, thus:
+
+```
+$ -d alpine cat /etc/os-release
+NAME="Alpine Linux"
+ID=alpine
+VERSION_ID=3.11.3
+PRETTY_NAME="Alpine Linux v3.11"
+HOME_URL="https://alpinelinux.org/"
+BUG_REPORT_URL="https://bugs.alpinelinux.org/"
+```
 
-This assumes, of course, that you already have genie installed and running correctly. If not, it won't work.
-genie 1.32 or higher is recommended, as earlier versions of genie had issues with arguments containing spaces.
-If `$ ls -la 'C:\Program Files\'` produces an error complaining that _ls_ can't find _/mnt/c/Program_, you need
-to upgrade your genie installation.
+Obviously, any distribution chosen by -d/--distro must have genie installed, or the command will fail.
 
 ## Examples
 
 <img src="runingenie.png" alt="example screenshot" />
 
+## Installation
+
+Grab the latest RunInGenie.zip from the Releases page, unzip it, and put the resulting $.exe somewhere on your PATH. Easy!
+
+This assumes, of course, that you already have genie installed and running correctly. If not, it won't work. genie 1.32 or higher is recommended, as earlier versions of genie had issues with arguments containing spaces. If `$ ls -la 'C:\Program Files\'` produces an error complaining that _ls_ can't find _/mnt/c/Program_, you need to upgrade your genie installation.
+
+## Configuration
+
+By default, RunInGenie uses the `sh` shell to execute commands (or to start when executed without parameters), and executes those commands in the WSL default distribution. These can be overridden by creating the JSON file `$.json` in the same directory as the `$.exe` executable, in the following format:
+
+```
+{
+  "shell":  "zsh",
+  "distro": "debian"
+}
+```
+
+Either or both options can be specified to change the defaults.
+
 ## Bugs
 
 Yes, there almost certainly are. Quoting is complicated.