Merge "First pass on updating README.md" am: a55e9e4f5e

Original change: https://android-review.googlesource.com/c/platform/tools/metalava/+/1999431

Change-Id: I115dd64f2018f1a919930bbacdcc9293a91b7338
diff --git a/README.md b/README.md
index cda1d4b..397de8d 100644
--- a/README.md
+++ b/README.md
@@ -1,24 +1,24 @@
 # Metalava
 
-(Also known as "doclava2", but deliberately not named doclava2 since crucially
-it does not generate docs; it's intended only for **meta**data extraction and
-generation.)
+Metalava is a metadata generator intended for JVM type projects. The main
+users of this tool are Android Platform and AndroidX libraries, however this
+tool also works on non-Android libraries.
 
-Metalava is a metadata generator intended for the Android source tree, used for
-a number of purposes:
+Metalava has many features related to API management. Some examples of the most
+commonly used ones are:
 
-* Allow extracting the API (into signature text files, into stub API files
-  (which in turn get compiled into android.jar, the Android SDK library) and
+* Allows extracting the API (into signature text files, into stub API files
+  which in turn get compiled into android.jar, the Android SDK library) and
   more importantly to hide code intended to be implementation only, driven by
-  javadoc comments like @hide, @$doconly, @removed, etc, as well as various
+  javadoc comments like @hide, @doconly, @removed, etc, as well as various
   annotations.
 
 * Extracting source level annotations into external annotations file (such as
   the typedef annotations, which cannot be stored in the SDK as .class level
-  annotations).
+  annotations) to ship alongside the Android SDK and used by Android Lint.
 
 * Diffing versions of the API and determining whether a newer version is
-  compatible with the older version. (See [COMPATIBILITY.md](COMPATIBILITY.md)))
+  compatible with the older version. (See [COMPATIBILITY.md](COMPATIBILITY.md))
 
 ## Building and running
 
@@ -29,11 +29,29 @@
     $ cd tools/metalava
     $ ./gradlew
 
-This builds a binary distribution in `../../out/host/common/install/metalava/bin/metalava`.
+It puts build artifacts in `../../out/metalava/`.
 
-To run metalava:
+To run the metalava executable:
 
-    $ ../../out/host/common/install/metalava/bin/metalava
+### Through Gradle 
+
+To list all the options:
+
+    $ ./gradlew run
+
+To run it with specific arguments:
+
+    $ ./gradlew run --args="--api path/to/api.txt"
+
+### Through distribution artifact
+
+First build it with:
+
+    $ ./gradlew installDist
+
+Then run it with:
+
+    $ ../../out/metalava/install/metalava/bin/metalava
                     _        _
      _ __ ___   ___| |_ __ _| | __ ___   ____ _
     | '_ ` _ \ / _ \ __/ _` | |/ _` \ \ / / _` |
@@ -55,25 +73,8 @@
 
 (*output truncated*)
 
-Metalava has a new command line syntax, but it also understands the doclava1
-flags and translates them on the fly. Flags that are ignored are listed on the
-command line. If metalava is dropped into an Android framework build for
-example, you'll see something like this (unless running with --quiet) :
-
-    metalava: Ignoring javadoc-related doclava1 flag -J-Xmx1600m
-    metalava: Ignoring javadoc-related doclava1 flag -J-XX:-OmitStackTraceInFastThrow
-    metalava: Ignoring javadoc-related doclava1 flag -XDignore.symbol.file
-    metalava: Ignoring javadoc-related doclava1 flag -doclet
-    metalava: Ignoring javadoc-related doclava1 flag -docletpath
-    metalava: Ignoring javadoc-related doclava1 flag -templatedir
-    metalava: Ignoring javadoc-related doclava1 flag -htmldir
-    ...
-
 ## Features
 
-* Compatibility with doclava1: in compat mode, metalava spits out the same
-  signature files for the framework as doclava1.
-
 * Ability to read in an existing android.jar file instead of from source, which
   means we can regenerate signature files etc for older versions according to
   new formats (e.g. to fix past errors in doclava, such as annotation instance