document the "issues" command

Author: nikomatsakis

src/admin/issues.md

@@ -0,0 +1,19 @@
+# Creating tracking issues
+
+Usage:
+
+```
+> cargo run -- issues
+```
+
+The `issues` command is used to create tracking issues at the start of a project goal session. When you first run it, it will simply tell you what actions it plans to take.
+
+To actually commit and create the issues, supply the `--commit` flag:
+
+```
+> cargo run -- issues --commit
+```
+
+This will also edit the goal documents to include a link to each created tracking issue. You should commit those edits.
+
+You can later re-run the command and it will not repeat actions it has already taken.c