improved documentation

docs/index.md

@@ -1,13 +1,39 @@
 ## semgrep-scalafix
 
+The goal of semgrep-scalafix is to provide scalafix rules for checks that exist as [semgrep rules](https://semgrep.dev/p/scala).
+
 ### Usage
 
 This library is currently available for Scala binary versions 2.13 and 3.1.
 
 To use the latest version, include the following in your `build.sbt`:
 
 ```scala
-libraryDependencies ++= Seq(
+ThisBuild / scalafixDependencies += 
   "com.banno" %% "semgrep-scalafix" % "@VERSION@"
-)
+```
+
+Once enabled, configure which rules scalafix will run by adding them to your `.scalafix.conf` file like so:
+```
+//.scalafix.conf
+rules = [
+  NoRsaWithoutPadding
+]
+```
+
+
+### Available Rules
+
+#### NoRsaWithoutPadding
+Relevant semgrep rule: [scala.lang.security.audit.rsa-padding-set.rsa-padding-set](https://semgrep.dev/r?q=scala.lang.security.audit.rsa-padding-set.rsa-padding-set).
+
+This scalafix rule will raise an error if a `javax.crypto.Cipher` is instantiated using RSA, any mode, with no padding. For example:
+
+```scala
+import javax.crypto.Cipher
+
+val badCipher = Cipher.getInstance("RSA/None/NoPadding") // will raise scalafix error
+val alsoBad   = Cipher.getInstance("RSA/ECB/NoPadding") // will raise scalafix error
+
+val goodCipher = Cipher.getInstance("RSA/ECB/PKCS1Padding") 
 ```