Add a transparent placeholder image for people.

This solves the 404 we're getting when we request non-existent pictures.

Author: jasongrout

_includes/biocard.html

@@ -1,11 +1,13 @@
 <section class="biocard">
-  <img
-    class="biocard-photo"
-    alt="{{ include.name }}"
-    width=160
-    height=160
-    src="/assets/bios/{{ include.photo }}"
-    loading="{% if include.loading %}{{ include.loading }}{% else %}lazy{% endif %}" />
+  {% if include.photo %}
+    <img
+      class="biocard-photo"
+      alt="{{ include.name }}"
+      width=160
+      height=160
+      src="/assets/bios/{{ include.photo }}"
+      loading="{% if include.loading %}{{ include.loading }}{% else %}lazy{% endif %}" />
+    {% endif %}
   <div class="biocard-copy">
     <div class="biocard-header">{{ include.name }}</div>
     {% if include.affiliation %}

about.html

@@ -286,8 +286,7 @@
 
 software_steering_council:
   - name: Eric Charles
-    photo:
-    twitter_handle:
+    photo: placeholder.png
     gh_handle: echarles
     subproject: Jupyter Notebook
   - name: Frédéric Collonval
@@ -301,8 +300,7 @@
     gh_handle: sylvaincorlay
     subproject: Voilà
   - name: Itay Dafna
-    photo:
-    twitter_handle:
+    photo: placeholder.png
     gh_handle: ibdafna
     subproject: Jupyter Widgets
   - name: Paul Ivanov
@@ -333,8 +331,7 @@
     twitter_handle: zrsailer
     subproject: Jupyter Server
   - name: Rick Wagner
-    photo:
-    twitter_handle:
+    photo: placeholder.png
     gh_handle: rpwagner
     subproject: Jupyter Security
   - name: Carol Willing