Improve build instructions (denoland#1593)

Docs.md

@@ -319,13 +319,20 @@ submodule. However, you need to install separately:
    [Not 3](https://github.com/denoland/deno/issues/464#issuecomment-411795578).
 4. [ccache](https://developer.mozilla.org/en-US/docs/Mozilla/Developer_guide/Build_Instructions/ccache)
    (Optional but helpful for speeding up rebuilds of V8.)
-5. Extra steps for Windows users:
-   1. Add `python.exe` to `PATH` (e.g. `set PATH=%PATH%;C:\Python27\python.exe`)
-   2. Get [VS Community 2017](https://www.visualstudio.com/downloads/). Make
-      sure to select the option to install C++ tools and the Windows SDK.
-   3. Enable `Debugging Tools for Windows`. Go to `Control Panel` ->
-      `Windows 10 SDK` -> Right-Click -> `Change` -> `Change` ->
-      `Check Debugging Tools for Windows` -> `Change` -> `Finish`.
+
+Extra steps for Mac users:
+
+1. [XCode](https://developer.apple.com/xcode/)
+2. Openssl 1.1: `brew install openssl@1.1` (TODO: shouldn't be necessary)
+
+Extra steps for Windows users:
+
+1. Add `python.exe` to `PATH` (e.g. `set PATH=%PATH%;C:\Python27\python.exe`)
+2. Get [VS Community 2017](https://www.visualstudio.com/downloads/). Make sure
+   to select the option to install C++ tools and the Windows SDK.
+3. Enable `Debugging Tools for Windows`. Go to `Control Panel` ->
+   `Windows 10 SDK` -> Right-Click -> `Change` -> `Change` ->
+   `Check Debugging Tools for Windows` -> `Change` -> `Finish`.
 
 ### Build:
 
@@ -334,6 +341,10 @@ submodule. However, you need to install separately:
     cd deno
     ./tools/setup.py
 
+    # You may need to ensure that sccache is running.
+    # (TODO it's unclear if this is necessary or not.)
+    # prebuilt/mac/sccache --start-server
+
     # Build.
     ./tools/build.py
 

README.md

@@ -85,6 +85,11 @@ Try it:
 See [deno_install](https://github.com/denoland/deno_install) for more
 installation methods..
 
+## Build locally (advanced users only)
+
+For instructions to build this project locally, please see
+[the docs](https://github.com/denoland/deno/blob/master/Docs.md#build-instructions-for-advanced-users-only).
+
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