Update issue templates

.github/ISSUE_TEMPLATE/pml1-figure-code.md

@@ -0,0 +1,18 @@
+---
+name: PML1 figure code
+about: " Use this template to specify a figure a code example is needed for."
+title: "[language] code for PML1 figure [figure-number]"
+labels: ''
+assignees: ''
+
+---
+
+<!--
+Substitute the `[language]` and `[figure-number]` placeholders in issue title for respectively
+the language the code to create the figure will be written in and the figure number in the
+format `[chapter].[figure]`.
+
+Assign the issue to yourself if you are planning on working on this figure code.
+
+The body of the issue can be left empty.
+-->