Document --singleton option

Author: kzu

readme.md

@@ -19,6 +19,7 @@ Arguments:
 
 Options:
   -s, --source <source>      NuGet feed to check for updates. [default: https://api.nuget.org/v3/index.json]
+  --singleton                Ensure a single tool process is running.
   -i, --interval <interval>  Time interval in seconds for the update checks. [default: 5]
   -f, --force                Stop all running tool processes to apply updates. [default: True]
   -q, --quiet                Do not display any informational messages.
@@ -32,8 +33,8 @@ Features:
 * Automatically exits if the tool also runs to completion
 * Forwards exit code from the tool
 * Restarts tool as needed to apply updates
-* Optionally stops all other tool running processes (for the same package id) before 
-  applying updates (`-f` option, to avoid errors when updating a running tool).
+* Stops all other tool running processes so updating succeeds (can be opted out with `-f=false`)
+* Ensures a single tool is running (`--singleton` option)
 * Passes all tool options verbatim (except for `evergreen` options, specified *before* the tool argument)
 * Automatically discovers tool *command* when it doesn't match the tool *package id* 
   (i.e. [dotnet-eventgrid](https://www.nuget.org/packages/dotnet-eventgrid) > `eventgrid`).
@@ -43,6 +44,7 @@ Features:
   [evergreen]
     interval = 5
     source = https://myfeed.com/index.json 
+    singleton = true
   ```