Merge bitcoin#15964: Docs: Improve build-osx document formatting

dbd137a Improve build-osx formatting (Giulio Lombardo)

Pull request description:

  This `PR` will improve `build-osx.md` formatting by:

  1. Updating Markdown syntax to the latest one
  2. Adding syntax highlighting to all code blocks
  3. Aligning the text up to `80` column guideline (before it was following different guidelines, sometime `80`, sometime `90`, etc.)
  4. Small grammar improvements here and there

ACKs for top commit:
  fanquake:
    ACK dbd137a - Document reads and renders essentially the same as the current `build-osx.md`, with minor formatting / grammatical  changes.

Tree-SHA512: 47747991b5fddf0725c82f17f153e83150e51f698787544b4c51b32479989e4b550e2b3aec92979d2b0c76edfdcbbe7c4d9d0115df12e2bfde0cfcb277e9b984

Author: fanquake

doc/build-osx.md

@@ -1,13 +1,17 @@
-macOS Build Instructions and Notes
-====================================
+# macOS Build Instructions and Notes
+
 The commands in this guide should be executed in a Terminal application.
-The built-in one is located in `/Applications/Utilities/Terminal.app`.
+The built-in one is located in
+```
+/Applications/Utilities/Terminal.app
+```
 
-Preparation
------------
+## Preparation
 Install the macOS command line tools:
 
-`xcode-select --install`
+```shell
+xcode-select --install
+```
 
 When the popup appears, click `Install`.
 
@@ -35,12 +39,12 @@ export PATH=$(echo "$PATH" | sed -e '/\\/!s/ /\\ /g') # fix whitespaces
 
 Next, follow the instructions in [build-generic](build-generic.md)
 
-Disable-wallet mode
---------------------
-When the intention is to run only a P2P node without a wallet, Dash Core may be compiled in
-disable-wallet mode with:
-
-    ./configure --disable-wallet
+## `disable-wallet` mode
+When the intention is to run only a P2P node without a wallet, Dash Core may be
+compiled in `disable-wallet` mode with:
+```shell
+./configure --disable-wallet
+```
 
 In this case there is no dependency on Berkeley DB 4.8.
 
@@ -52,18 +56,21 @@ Running
 Dash Core is now available at `./src/dashd`
 
 Before running, you may create an empty configuration file:
+```shell
+mkdir -p "/Users/${USER}/Library/Application Support/DashCore"
 
-    mkdir -p "/Users/${USER}/Library/Application Support/DashCore"
-
-    touch "/Users/${USER}/Library/Application Support/DashCore/dash.conf"
+touch "/Users/${USER}/Library/Application Support/DashCore/dash.conf"
 
-    chmod 600 "/Users/${USER}/Library/Application Support/DashCore/dash.conf"
+chmod 600 "/Users/${USER}/Library/Application Support/DashCore/dash.conf"
+```
 
-The first time you run dashd, it will start downloading the blockchain. This process could take many hours, or even days on slower than average systems.
+The first time you run dashd, it will start downloading the blockchain. This process could
+take many hours, or even days on slower than average systems.
 
 You can monitor the download process by looking at the debug.log file:
-
-    tail -f $HOME/Library/Application\ Support/DashCore/debug.log
+```shell
+tail -f $HOME/Library/Application\ Support/DashCore/debug.log
+```
 
 Other commands:
 -------