docs: update STYLE.md (#87)

Signed-off-by: Michael Rebello <mrebello@lyft.com>
Signed-off-by: JP Simard <jp@jpsim.com>

mobile/STYLE.md

@@ -1,13 +1,22 @@
-# Envoy Mobile style guide
-
 ## C++ coding style
 
-* C++ code uses the [Envoy style guide](https://github.com/envoyproxy/envoy/blob/master/STYLE.md)
+- C++ code uses the [Envoy style guide](https://github.com/envoyproxy/envoy/blob/master/STYLE.md)
+- Code is auto-formatted using `clang-format` with [these rules](./.clang-format)
 
-## Swift coding style
+## Java coding style
+
+- Java code is auto-formatted using `clang-format` with [these rules](./.clang-format)
+
+## Objective-C coding style
 
-* TODO(rebello95): Fill this in.
+- Objective-C code is auto-formatted using `clang-format` with [these rules](./.clang-format)
 
 ## Kotlin coding style
 
-* TODO(buildbreaker): Fill this in.
+- TODO(buildbreaker): Fill this in after https://github.com/lyft/envoy-mobile/issues/27
+
+## Swift coding style
+
+- Swift code style is validated using [SwiftLint](https://github.com/realm/swiftlint)
+- The rules enforced are available in the repo's [.swiftlint.yml file](./.swiftlint.yml)
+- The linter may be run locally using `swiftlint` or auto-corrected with `swiftlint autocorrect`