Fix README image URLs for master branch

Author: jonathanvdc

README.md

@@ -57,49 +57,49 @@ dotnet add package Pixie.Loyc
 
 Pixie has built-in support for caret diagnostics. It can highlight a source region, emphasize the most relevant span, and render line numbers with surrounding context.
 
-![Diagnostic](https://raw.githubusercontent.com/jonathanvdc/Pixie/main/docs/img/caret.svg)
+![Diagnostic](https://raw.githubusercontent.com/jonathanvdc/Pixie/master/docs/img/caret.svg)
 
 ### Argument parsing with feedback
 
 Pixie can parse GNU-style command-line options and report mistakes in a user-friendly way, including usage guidance and option name suggestions.
 
-![Option parsing feedback](https://raw.githubusercontent.com/jonathanvdc/Pixie/main/docs/img/option-parsing-feedback.svg)
+![Option parsing feedback](https://raw.githubusercontent.com/jonathanvdc/Pixie/master/docs/img/option-parsing-feedback.svg)
 
 ### Help messages
 
 Pixie can generate help output from the same option definitions you use for parsing, so parsing and documentation stay in sync.
 
-![Help message](https://raw.githubusercontent.com/jonathanvdc/Pixie/main/docs/img/help-message.svg)
+![Help message](https://raw.githubusercontent.com/jonathanvdc/Pixie/master/docs/img/help-message.svg)
 
 ### Graceful terminal degradation
 
 Pixie tries to produce the nicest output your terminal can handle. When Unicode characters or ANSI styling are unavailable, it falls back to simpler representations instead of breaking formatting.
 
 Unicode-rich rendering:
 
-![Fancy bullets](https://raw.githubusercontent.com/jonathanvdc/Pixie/main/docs/img/degradation-fancy.svg)
+![Fancy bullets](https://raw.githubusercontent.com/jonathanvdc/Pixie/master/docs/img/degradation-fancy.svg)
 
 Simpler fallback rendering:
 
-![Simple bullets](https://raw.githubusercontent.com/jonathanvdc/Pixie/main/docs/img/degradation-simple.svg)
+![Simple bullets](https://raw.githubusercontent.com/jonathanvdc/Pixie/master/docs/img/degradation-simple.svg)
 
 ### Readable layout
 
 Pixie supports alignment, wrapping, and reusable markup nodes for common CLI output patterns.
 
 Without careful layout, terminal messages can become awkward:
 
-![Sad line break](https://raw.githubusercontent.com/jonathanvdc/Pixie/main/docs/img/sad-line-break.svg)
+![Sad line break](https://raw.githubusercontent.com/jonathanvdc/Pixie/master/docs/img/sad-line-break.svg)
 
 With Pixie, the same message can be wrapped and structured more cleanly:
 
-![Happy line break](https://raw.githubusercontent.com/jonathanvdc/Pixie/main/docs/img/happy-line-break.svg)
+![Happy line break](https://raw.githubusercontent.com/jonathanvdc/Pixie/master/docs/img/happy-line-break.svg)
 
 ### Loyc interoperability
 
 If you use Loyc libraries such as EC# or LeMP, `Pixie.Loyc` can translate their diagnostics into Pixie markup so they render consistently with the rest of your application output.
 
-![Loyc diagnostic](https://raw.githubusercontent.com/jonathanvdc/Pixie/main/docs/img/loyc-interop.svg)
+![Loyc diagnostic](https://raw.githubusercontent.com/jonathanvdc/Pixie/master/docs/img/loyc-interop.svg)
 
 ## Getting started