Add 'cp' (Carpentry) as a new lesson type

* Add 'cp' (Carpentry) as a lesson type (for instructor training)
* Explain lesson type abbreviations (swc, dc, lc, cp)
* Emphasize the fact that there is no need to edit "repository" variable in front matter

bin/boilerplate/_config.yml

@@ -2,7 +2,11 @@
 # Values for this lesson.
 #------------------------------------------------------------
 
-# Which carpentry is this ("swc", "dc", or "lc")?
+# Which carpentry is this ("swc", "dc", "lc", or "cp")?
+# swc: Software Carpentry
+# dc: Data Carpentry
+# lc: Library Carpentry
+# cp: Carpentries (to use for instructor traning for instance)
 carpentry: "swc"
 
 # Overall title for pages.
@@ -20,6 +24,7 @@ kind: "lesson"
 
 # Magic to make URLs resolve both locally and on GitHub.
 # See https://help.github.com/articles/repository-metadata-on-github-pages/.
+# Please don't change it: <USERNAME>/<PROJECT> is correct.
 repository: <USERNAME>/<PROJECT>
 
 # Sites.

bin/lesson_check.py

@@ -171,7 +171,7 @@ def check_config(reporter, source_dir):
     reporter.check_field(config_file, 'configuration',
                          config, 'kind', 'lesson')
     reporter.check_field(config_file, 'configuration',
-                         config, 'carpentry', ('swc', 'dc', 'lc'))
+                         config, 'carpentry', ('swc', 'dc', 'lc', 'cp'))
     reporter.check_field(config_file, 'configuration', config, 'title')
     reporter.check_field(config_file, 'configuration', config, 'email')