Reordered intro section and added description on build runtime to REA…

…DME.md.

PiperOrigin-RevId: 476474167

README.md

@@ -9,8 +9,8 @@
 ## What is XLS?
 
 XLS implements a High Level Synthesis (HLS) toolchain which produces
-synthesizable designs (Verilog and SystemVerilog) from flexible, high-level 
-descriptions of functionality. It is fully Open Source: Apache 2 licensed and 
+synthesizable designs (Verilog and SystemVerilog) from flexible, high-level
+descriptions of functionality. It is fully Open Source: Apache 2 licensed and
 developed via GitHub.
 
 XLS (Accelerated HW Synthesis) aims to be the Software Development Kit (SDK) for

docs_src/README.md

@@ -8,6 +8,11 @@
 
 ## What is XLS?
 
+XLS implements a High Level Synthesis (HLS) toolchain which produces
+synthesizable designs (Verilog and SystemVerilog) from flexible, high-level
+descriptions of functionality. It is fully Open Source: Apache 2 licensed and
+developed via GitHub.
+
 XLS (Accelerated HW Synthesis) aims to be the Software Development Kit (SDK) for
 the End of Moore's Law (EoML) era. In this "age of specialization", software and
 hardware engineers must do more co-design across their domain boundaries --
@@ -22,10 +27,6 @@ source can also be used to generate hardware block output -- the XLS tools'
 correctness ensures (and provides tools to help formally verify) that they are
 functionally identical.
 
-XLS implements a High Level Synthesis (HLS) toolchain which produces
-synthesizable designs from flexible, high-level descriptions of functionality.
-It is fully Open Source: Apache 2 licensed and developed via GitHub.
-
 XLS is used inside of Google for generating feed-forward pipelines from
 "building block" routines / libraries that can be easily retargeted, reused, and
 composed in a latency-insensitive manner.
@@ -55,6 +56,9 @@ The following instructions are for the Ubuntu 20.04 (Focal Fossa) and Ubuntu
 
 We start by assuming
 [Bazel has been installed](https://bazel.build/install/ubuntu).
+On an average 8-core VM, a full initial build (including the C++ frontend) may take up to 6 hours.
+A build without the C++ frontend may take about 2 hours. Please see the two corresponding
+command lines below:
 
 ```console
 ~$ git clone https://github.com/google/xls.git
@@ -68,10 +72,16 @@ bazel 5.2.0
 
 ~/xls$ # Note we're going to tell Ubuntu that `/usr/bin/env python` is actually python3
 ~/xls$ # here, since that is not the case by default on Ubuntu 20.04.
+~/xls$ # This is important. Without this step, you may experience cryptic error messages:
 ~/xls$ sudo apt install python3-distutils python3-dev libtinfo5 python-is-python3
 
-~/xls$ # Now build/test everything in optimized build mode.
-~/xls$ bazel test -c opt //...
+~/xls$ # Now build/test in optimized build mode.
+~/xls$ # If you don't plan on using the C++ frontend, which is not needed to get started,
+~/xls$ # use this command line:
+~/xls$ bazel test -c opt -- //xls/... -//xls/contrib/xlscc/...
+
+~/xls$ # To build everything, including the C++ frontend:
+~/xls$ bazel test -c opt -- //xls/...
 ```
 
 Reference build/test environment setups are also provided via `Dockerfile`s: