feat: Spectroscopy with SDSS tutorial (#28)

Follow-up to JuliaAstro/JuliaAstro.github.io#203

Trying it out in notebook format

Doc preview:
https://learn.juliaastro.org/previews/PR28/tutorials/spectroscopy-sdss/

---------

Co-authored-by: Chris Garling <chris.t.garling@gmail.com>

Author: icweaver

src/assets/spec-SDSS.png

@@ -9,6 +9,9 @@
 section#title {
     display: none !important;
 }
+featured-card .author {
+    display: none !important;
+}
 </style>
 
 <meta name="pluto-insertion-spot-meta">

src/index.html

@@ -26,6 +26,11 @@
             "title": "Dust",
             "description": "Extinction and attenuation curves.",
             "tags": ["dust"]
+        },
+        {
+            "title": "Spectroscopy",
+            "description": "Spectroscopy.",
+            "tags": ["spectroscopy"]
         }
     ]
 }

src/pluto_export_configuration.json

@@ -1,4 +1,4 @@
-sections = ["file I/O", "units", "models", "cosmology", "dust"]
+sections = ["file I/O", "units", "models", "cosmology", "dust", "spectroscopy"]
 
 Dict(
     "main" => [uppercase(section) => collections[section].pages for section in sections],