Updated spack setup page. (#824)

Squashed 10 commits:

getting_started/spack.md: incorporate feedback
* Thanks to Claire Carouge, Chris Bull and Davide Marchegiani.

Changed '/home/565/davide' with '/Users/davide' in 'how to build a model' page

Moved CSS styles to 'access-nri.css'. Minor fixes in the styles for 'how to build a model'.

Added coloured outputs

Fix colours for spack output

Added Spencer's suggestions

Added specification of step not require in admonition of 'how to build a mode' page

Added Spencer's suggestion on liinking the 'how to run a model page'

Fixed compiler in install output

Fixed /Users/davide. Fixed architecture.

docs/css/access-nri.css

@@ -1088,6 +1088,39 @@ img.terminalSwitch:hover {
   cursor: pointer;
 }
 
+/* =============================================================== 
+  Virtural terminal colours for Spack output
+*/
+
+.spack-red {
+  color: #FF6E67;
+}
+.spack-highlighted {
+  color: #FFFFFF;
+  font-weight: 600;
+}
+.spack-cyan {
+  color: cyan;
+}
+.spack-indigo {
+  color: #6871FF;
+}
+.spack-green{
+  color: #00C200;
+}
+.spack-pink {
+  color: #CA30C7;
+}
+.spack-grey {
+  color: #686868;
+}
+
+.spack::part(directory),
+.spack ::part(directory) {
+  color: #60FA67;
+}
+
+
 /* =============================================================== 
   General styling for html tabs
 */
@@ -1156,6 +1189,10 @@ img.terminalSwitch:hover {
 /* =============================================================== 
   Miscellaneous
 */
+.keep-blanks {
+  white-space: pre;
+}
+
 .centered {
   display: block;
   margin-left: auto;