docs: how to opt out of precompiled artefacts (#240)

Author: cocoa-xu

README.md

@@ -42,13 +42,26 @@ end
 
 ## Configuration
 
+### Runtime Configuration
+
 ```elixir
 config :exqlite, default_chunk_size: 100
 ```
 
 * `default_chunk_size` - The chunk size that is used when multi-stepping when
   not specifying the chunk size explicitly.
+  
+### Compile-time Configuration
+
+In `config/config.exs`,
+
+```elixir
+config :exqlite, make_force_build: false
+```
 
+* `make_force_build` - Set `true` to opt out of using precompiled artefacts.
+This option only affects the default configuration. For advanced configuation,
+this library will always compile natively.
 
 ## Advanced Configuration