Add docs for experimental_use_abi_jars (#446)

CompileAvoidance.md

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+[![Build Status](https://badge.buildkite.com/a8860e94a7378491ce8f50480e3605b49eb2558cfa851bbf9b.svg)](https://buildkite.com/bazel/kotlin-postsubmit)
+
+# Compilation Avoidance
+
+# ABI support
+
+**rules_kotlin** now supports compilation avoidance through the use of ABI jars (also known as
+interface or header jars) for classpath dependencies. This can have significant performance wins for
+non-ABI affecting changes since down stream recompilation can be avoided in such cases. 
+
+This feature can be enabled through the `experimental_use_abi_jars` flag in the tool chain as
+follows
+
+```python
+load("//kotlin:kotlin.bzl", "define_kt_toolchain")
+
+
+define_kt_toolchain(
+    name = "kotlin_toolchain",
+    experimental_use_abi_jars = True,
+)
+```
+
+This feature is implemented using the Jetbrains Kotlin JvmABI compiler plugin for generating headers
+for Kotlin code. Unfortunately there are some known bugs with this plugin that affect less than 1%
+of targets.
+* https://youtrack.jetbrains.com/issue/KT-40340
+* https://youtrack.jetbrains.com/issue/KT-40133
+
+If you encounter such bugs, ABI generation can be disabled on a per target basis by setting the
+following tag
+
+```python
+load("//kotlin:kotlin.bzl", "kt_jvm_library")
+
+kt_jvm_library(
+    name = "framework",
+    tags = ["kt_abi_plugin_incompatible"],
+)
+```