Add MongoDB skill.

_data/skills.yaml

@@ -123,8 +123,12 @@ categories:
     img: skills/libraries/postgres.svg
   - id: appengine
     proficiency: 3
-    name: App Engine/Datastore
+    name: AppEngine
     img: skills/libraries/appengine.png
+  - id: mongodb
+    proficiency: 1
+    name: MongoDB
+    img: skills/libraries/mongodb.png
 - id: tools
   title: Tools
   skills:

_includes/components/footer.njk

@@ -39,6 +39,7 @@
   <p>PostgreSQL logo from <a href="https://www.postgresql.jp/npo/logo/?searchterm=logo">the PostgreSQL JP site</a>.</p>
   <p>Eleventy logo from <a href="https://11ty.io">the Eleventy site</a>.</p>
   <p>AppEngine logo from <a href="https://favpng.com/png_view/engine-google-app-engine-google-cloud-platform-google-compute-engine-cloud-computing-png/NgfHuMDX">FavPNG</a>.</p>
+  <p>MongoDB logo from <a href="https://favpng.com/png_view/bay-leaves-mongodb-inc-computer-software-business-software-developer-png/sGC75bKw">FavPNG</a>.</p>
 
   <p>Git logo from <a href="https://git-scm.com/downloads/logos">the Git logo page</a>.</p>
   <p>Mercurial logo from <a href="https://www.selenic.com/hg-logo/">the Mercurial logo page</a>.</p>