Added custom token support

README.md

@@ -296,6 +296,39 @@ Dutch Passport Numbers (9 alphanumeric characters
 Dutch Identification Document Numbers (varying formats)
 Custom keywords specified in LoggerSettings
 
+Header tokens:
+
+{date} {time} {ts} {tz} {unix} {ticks}{newline}
+{sev} {category} {env}{newline}
+{host} {machine}{newline}
+{process} {pid} {procstart} {uptime}{newline}
+{thread} {threadname} {task}{newline}
+{user}{newline}
+{app} {appbase} {domain}{newline}
+{framework} {os} {arch}{newline}
+{mem} {gc}{newline}
+{cwd}
+
+Example of custom header:
+```csharp
+[Date: 2026-01-30] [Time: 14:22:11.384] [2026-01-30 14:22:11.384] [UTC] [Unix: 1738246931] [Ticks: 638422525313840000]
+[Severity: Info] [Category: Startup] [Env: Production]
+[Host: api-01] [Machine: API-SERVER-01]
+[Process: MyService] [PID: 4216] [ProcStart: 2026-01-30T14:20:03.5123456Z] [Uptime: 128s]
+[Thread: 9] [ThreadName: worker-1] [TaskId: 42]
+[User: svc-api]
+[App: MyService.exe] [AppBase: C:\apps\myservice\] [Domain: 1]
+[Runtime: .NET 8.0.1] [OS: Linux 6.6.9] [Arch: X64]
+[Memory: 128MB] [GC: 12/4/1]
+[CWD: /app]
+```
+
+Add Custom tokens:
+
+```csharp
+Logger.LoggerSettings.HeaderTokens.AddCustomToken("spaceShuttleId", context => $"[Shuttle: {context.SpaceShuttleId}]");
+```
+
 
 **Code for enabling GrayLog in the above *advanced* logger class:**