README: unify command line instructions

Consistently indicate whether the command requires super-user
permission by prefixing commands with `sudo`.

Despite my preference for the conventional use of the pseuod-prompts (`$` and
`#`) I think they should be removed, as they end up in the way for those users
who like to copy-paste commands to their terminals. Moreover, Github seems to
interpret the latter as shell comment, and renders `#`-prefixed lines as
comments.

`apt install` instructions are broken on multiple lines, and package names
sorted alphabetically.

Author: dacav

README

@@ -22,31 +22,31 @@ list is available below.
 
 [source, console]
 ----
-$ sudo apt install libpam-u2f pamu2fcfg
+sudo apt install libpam-u2f pamu2fcfg
 ----
 
 Additionally, Yubico maintains a PPA with up-to-date versions of pam-u2f.
 
 [source, console]
 ----
-$ sudo apt install software-properties-common
-$ sudo apt-add-repository ppa:yubico/stable
-$ sudo apt update
-$ sudo apt install libpam-u2f pamu2fcfg
+sudo apt install software-properties-common
+sudo apt-add-repository ppa:yubico/stable
+sudo apt update
+sudo apt install libpam-u2f pamu2fcfg
 ----
 
 === Fedora
 
 [source, console]
 ----
-$ sudo dnf install pam-u2f pamu2fcfg
+sudo dnf install pam-u2f pamu2fcfg
 ----
 
 === macOS
 
 [source, console]
 ----
-$ brew install pam-u2f
+brew install pam-u2f
 ----
 
 [[building]]
@@ -62,16 +62,23 @@ installed using
 
 [source, console]
 ----
-# apt install --no-install-recommends autoconf automake libtool pkg-config \
-    libfido2-dev libpam-dev libssl-dev
+sudo apt install --no-install-recommends \
+    autoconf \
+    automake \
+    libfido2-dev \
+    libpam-dev \
+    libssl-dev \
+    libtool \
+    pkg-config \
+;
 ----
 
 If you downloaded a tarball, build it as follows.
 
 [source, console]
 ----
-$ ./configure
-$ make
+./configure
+make
 ----
 
 Once the module is built, copy the file `pam_u2f.so` to the correct
@@ -87,14 +94,14 @@ You may check out the sources using Git with the following command:
 
 [source, console]
 ----
-$ git clone https://github.com/Yubico/pam-u2f.git
+git clone https://github.com/Yubico/pam-u2f.git
 ----
 
 This will create a directory 'pam-u2f'. Enter the directory:
 
 [source, console]
 ----
-$ cd pam-u2f
+cd pam-u2f
 ----
 
 `autoconf`, `automake`, `libtool`, and `libpam` must be installed.
@@ -103,24 +110,41 @@ the necessary dependencies can be installed using
 
 [source, console]
 ----
-# apt install --no-install-recommends autoconf automake libtool \
-    pkg-config libfido2-dev libpam-dev libssl-dev asciidoc xsltproc \
-    libxml2-utils docbook-xml
+sudo apt install --no-install-recommends
+    asciidoc \
+    autoconf \
+    automake \
+    docbook-xml \
+    libfido2-dev \
+    libpam-dev \
+    libssl-dev \
+    libtool \
+    libxml2-utils \
+    pkg-config \
+    xsltproc \
+;
 ----
 
 On Fedora, the necessary dependencies can be installed using
 
 [source, console]
 ----
-# dnf -y install autoconf automake libtool libfido2-devel pam-devel \
-    openssl-devel asciidoc
+sudo dnf -y install \
+    asciidoc \
+    autoconf \
+    automake \
+    libfido2-devel \
+    libtool \
+    openssl-devel \
+    pam-devel \
+;
 ----
 
 Generate the build system using:
 
 [source, console]
 ----
-$ autoreconf --install
+autoreconf --install
 ----
 
 Then build as usual, see above under <<building,Building from a source tarball>>.
@@ -406,7 +430,7 @@ configuration tool provided with the module:
 
 [source, console]
 ----
-$ pamu2fcfg -uusername -opam://myorigin -ipam://myappid
+pamu2fcfg -uusername -opam://myorigin -ipam://myappid
 ----
 
 the tool will register a connected token by using the specified origin
@@ -430,7 +454,7 @@ It is then possible to generate a credential file with:
 
 [source, console]
 ----
-$ ssh-keygen -t ecdsa-sk -f ./credential.ssh
+ssh-keygen -t ecdsa-sk -f ./credential.ssh
 ----
 
 Supported key types are ecdsa-sk and ed25519-sk. Note that passphrase protected