docs(readme): add PowerShell, replace example

Emphasize initool never changes the input file.

README.md

@@ -12,6 +12,8 @@ Rather than modify an INI file in place, it prints the modified contents of the
     - [POSIX](#posix)
     - [Windows](#windows)
     - [Both](#both)
+      - [PowerShell](#powershell)
+      - [Most shells](#most-shells)
   - [Whitespace](#whitespace)
   - [Nonexistent sections and properties](#nonexistent-sections-and-properties)
   - [Unparsable lines](#unparsable-lines)
@@ -53,6 +55,7 @@ The global options `-i`/`--ignore-case` and `-p`/`--pass-through` must precede t
 When given a valid command, initool first reads the INI file `filename` in its entirety.
 If the filename is `-`, initool reads standard input. For the commands `get`, `set`, `replace`, and `delete`, it then prints to standard output the file's contents with the desired change.
 For `exists`, it reports whether the section or the property exists through its exit status.
+**Initool never modifies the original file.**
 
 An INI file consists of properties (`key=value` lines) and sections (designated with a `[section name]` header line).
 A property can be at the "top level" of the file (before any section headers) or in a section (after a section header).
@@ -133,16 +136,66 @@ move /y settings.ini.new settings.ini
 
 #### Both
 
+##### PowerShell
+
+You can use pipelines in PowerShell without the issues with `cmd.exe`.
+The variable `$?` will be `True` only if all commands in the pipeline succeed.
+
+```powershell
+# We assume `initool.exe` (Windows) or the binary `initool` (Linux and macOS)
+# is in the current directory.
+./initool delete settings.ini test | ./initool set - '' cache 1024 > settings.ini.new
+if ($?) { move -Force settings.ini.new settings.ini }
+```
+
+### Most shells
+
+These examples work in POSIX-compatible shells, fish, `cmd.exe`, PowerShell, and others.
+The `>` at the beginning of the line represents the shell's prompt.
+
 To retrieve only the value of a property rather than the whole property (the section, key, and value), use the flag `-v` or `--value-only`:
 
 ```sh
-$ initool get tests/test.ini foo name1
+> initool get tests/test.ini foo name1
 [foo]
 name1=foo1
-$ initool get tests/test.ini foo name1 --value-only
+> initool get tests/test.ini foo name1 --value-only
 foo1
 ```
 
+To replace text in a value, use `replace`.
+
+```sh
+> initool get tests/replace-part.ini
+key=A longer value.
+another-key=ABAABBAAABBB
+empty=
+> initool replace tests/replace-part.ini "" key value string > updated.ini
+```
+
+The text of `updated.ini` will be:
+
+```ini
+key=A longer string.
+another-key=ABAABBAAABBB
+empty=
+```
+
+Now let's change the value of the key `empty`,
+but only if it is empty.
+
+```sh
+> ./initool replace tests/replace-part.ini "" empty "" no > updated.ini
+```
+
+The text of `updated.ini` will be:
+
+```ini
+key=A longer value.
+another-key=ABAABBAAABBB
+empty=no
+```
+
 ### Whitespace
 
 Initool defines whitespace as any mix of space and tab characters.