Make the getting started section in the README better

Some of my colleagues have commented in the past few months that the
Breakpad README is not very clear on how to get and build the code
nowadays. This change moves some of the docs from the "request
change review" section up to the "getting started" section, and adds
a few more things to clarify.

R=vapier@chromium.org
BUG=

Review URL: https://codereview.chromium.org/2035103002 .

README.md

@@ -10,41 +10,71 @@ crash-reporting system.
 * Developer/Reviews: [google-breakpad-dev@googlegroups.com](https://groups.google.com/d/forum/google-breakpad-dev)
 * Tests: [![Build Status](https://travis-ci.org/google/breakpad.svg?branch=master)](https://travis-ci.org/google/breakpad)
 
-## Getting started in 32-bit mode (from trunk)
+## Getting started (from master)
+
+1.  First, [download depot_tools](http://dev.chromium.org/developers/how-tos/install-depot-tools)
+    and ensure that they're in your `PATH`.
+
+2.  Create a new directory for checking out the source code (it must be named
+    breakpad).
+
+    ```sh
+    mkdir breakpad && cd breakpad
+    ```
+
+3.  Run the `fetch` tool from depot_tools to download all the source repos.
+
+    ```sh
+    fetch breakpad
+    cd src
+    ```
+
+4.  Build the source.
+
+    ```sh
+    ./configure && make
+    ```
+
+    You can also cd to another directory and run configure from there to build
+    outside the source tree.
+
+    This will build the processor tools (`src/processor/minidump_stackwalk`,
+    `src/processor/minidump_dump`, etc), and when building on Linux it will
+    also build the client libraries and some tools
+    (`src/tools/linux/dump_syms/dump_syms`,
+    `src/tools/linux/md2core/minidump-2-core`, etc).
+
+5.  Optionally, run tests.
 
     ```sh
-# Configure
-CXXFLAGS=-m32 CFLAGS=-m32 CPPFLAGS=-m32 ./configure
-# Build
-make
-# Test
     make check
-# Install
+    ```
+
+6.  Optionally, install the built libraries
+
+    ```sh
     make install
     ```
 
 If you need to reconfigure your build be sure to run `make distclean` first.
 
-## To request change review:
+To update an existing checkout to a newer revision, you can
+`git pull` as usual, but then you should run `gclient sync` to ensure that the
+dependent repos are up-to-date.
 
-1.  Get a copy of depot_tools repo.
+## To request change review
-    http://dev.chromium.org/developers/how-tos/install-depot-tools
 
-2.  Create a new directory for checking out the source code.
+1.  Follow the steps above to get the source and build it.
-    mkdir breakpad && cd breakpad
 
-3.  Run the `fetch` tool from depot_tools to download all the source repos.
+2.  Make changes. Build and test your changes.
-    `fetch breakpad`
-
-4.  Make changes. Build and test your changes.
     For core code like processor use methods above.
     For linux/mac/windows, there are test targets in each project file.
 
-5.  Commit your changes to your local repo and upload them to the server.
+3.  Commit your changes to your local repo and upload them to the server.
     http://dev.chromium.org/developers/contributing-code
     e.g. `git commit ... && git cl upload ...`
     You will be prompted for credential and a description.
 
-6.  At https://codereview.chromium.org/ you'll find your issue listed; click on
+4.  At https://codereview.chromium.org/ you'll find your issue listed; click on
     it, and select Publish+Mail, and enter in the code reviewer and CC
     google-breakpad-dev@googlegroups.com