Merge pull request #91 from mhwombat/master

Miscellaneous minor clarifications

pills/03-enter-environment.xml

@@ -343,6 +343,8 @@
 
     <para>
       This is quite similar to <command>apt-get update</command>.
+      (See <link xlink:href="https://nixos.wiki/wiki/Cheatsheet">this table</link>
+      for a rough mapping between Ubuntu and NixOS package management.)
     </para>
   </section>
 

pills/03/install-hello.txt

@@ -1,4 +1,5 @@
 $ nix-env -i hello
 installing 'hello-2.10'
+[...]
 building '/nix/store/0vqw0ssmh6y5zj48yg34gc6macr883xk-user-environment.drv'...
 created 36 symlinks in user environment

pills/04-basics-of-language.xml

@@ -62,6 +62,8 @@
       Launch <literal>nix repl</literal>. First of all, Nix supports basic arithmetic operations:
       <literal>+</literal>, <literal>-</literal>, and <literal>*</literal>. Integer division can be
       done with <literal>builtins.div</literal>.
+      (To exit <literal>nix repl</literal>, use the command <literal>:q</literal>.
+      Help is available through the <literal>:?</literal> command.)
     </para>
 
     <screen><xi:include href="./04/basics.txt" parse="text" /></screen>

pills/07-working-derivation.xml

@@ -65,6 +65,9 @@
 
       <programlisting><xi:include href="./07/builder.sh.txt" parse="text" /></programlisting>
 
+      The command <literal>declare -xp</literal>
+      lists exported variables.
+      (<literal>declare</literal> is a builtin bash function.)
       As we covered in the previous pill, Nix computes the output path of the
       derivation. The resulting <literal>.drv</literal> file contains a list of
       environment variables passed to the builder. One of these is