update extension README

Author: matthewbastien

lldb/tools/lldb-dap/README.md

@@ -65,6 +65,19 @@ This will attach to a process `a.out` whose process ID is 123:
 }
 ```
 
+You can also use the variable substituion `${command:PickProcess}` to select a
+process at the start of the debug session instead of setting the pid manually:
+
+```javascript
+{
+  "type": "lldb-dap",
+  "request": "attach",
+  "name": "Attach to PID",
+  "program": "/tmp/a.out",
+  "pid": "${command:PickProcess}"
+}
+```
+
 #### Attach by Name
 
 This will attach to an existing process whose base
@@ -224,7 +237,7 @@ the following `lldb-dap` specific key/value pairs:
 | Parameter                         | Type        | Req |         |
 |-----------------------------------|-------------|:---:|---------|
 | **program**                       | string      |     | Path to the executable to attach to. This value is optional but can help to resolve breakpoints prior the attaching to the program.
-| **pid**                           | number      |     | The process id of the process you wish to attach to. If **pid** is omitted, the debugger will attempt to attach to the program by finding a process whose file name matches the file name from **porgram**. Setting this value to `${command:pickMyProcess}` will allow interactive process selection in the IDE.
+| **pid**                           | number      |     | The process id of the process you wish to attach to. If **pid** is omitted, the debugger will attempt to attach to the program by finding a process whose file name matches the file name from **program**. Setting this value to `${command:PickProcess}` will allow interactive process selection in the IDE.
 | **waitFor**                       | boolean     |     | Wait for the process to launch.
 | **attachCommands**                | [string]    |     | LLDB commands that will be executed after **preRunCommands** which take place of the code that normally does the attach. The commands can create a new target and attach or launch it however desired. This allows custom launch and attach configurations. Core files can use `target create --core /path/to/core` to attach to core files.