Document octal and binary integer literals in syntax.

Also add a release notes snippet for it.

docs/markdown/Syntax.md

@@ -64,6 +64,13 @@ Hexadecimal literals are supported since version 0.45.0:
 int_255 = 0xFF
 ```
 
+Octal and binary literals are supported since version 0.47.0:
+
+```meson
+int_493 = 0o755
+int_1365 = 0b10101010101
+```
+
 Strings can be converted to a number like this:
 
 ```meson

docs/markdown/snippets/integer-base.md

@@ -0,0 +1,9 @@
+## Octal and binary string literals
+
+Octal and binary integer literals can now be used in build and option files.
+
+```meson
+int_493 = 0o755
+int_1365 = 0b10101010101
+```
+