docs(guide): add guide for IniBuilder

Author: Qard

guide/src/ini-builder.md

@@ -0,0 +1,37 @@
+# INI Builder
+
+When configuring a SAPI you may use `IniBuilder` to load INI settings as text.
+This is useful for setting up configurations required by the SAPI capabilities.
+
+INI settings applied to a SAPI through `sapi.ini_entries` will be immutable,
+meaning they cannot be changed at runtime. This is useful for applying settings
+to match hard requirements of the way your SAPI works.
+
+To apply _configurable_ defaults it is recommended to use a `sapi.ini_defaults`
+callback instead, which will allow settings to be changed at runtime.
+
+```rust,no_run
+use ext_php_rs::builder::{IniBuilder, SapiBuilder};
+
+// Create a new IniBuilder instance.
+let mut builder = IniBuilder::new();
+
+// Append a single key/value pair to the INIT buffer with an unquoted value.
+builder.unquoted("log_errors", "1");
+
+// Append a single key/value pair to the INI buffer with a quoted value.
+builder.quoted("default_mimetype", "text/html");
+
+// Append INI line text as-is. A line break will be automatically appended.
+builder.define("memory_limit=128MB");
+
+// Prepend INI line text as-is. No line break insertion will occur.
+builder.prepend("error_reporting=0\ndisplay_errors=1\n");
+
+// Construct a SAPI.
+let mut sapi = SapiBuiler::new("name", "pretty_name").build()
+  .expect("should build SAPI");
+
+// Dump INI entries from the builder into the SAPI.
+sapi.ini_entries = builder.finish();
+```