* Added starting files for Singularity-related KB (WIP).

singularity/20200710.Singularity-def-basics.md

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+Basics of Singularity Def File
+==============================
+
+[20200710]
+
+Definitive guide (the doc):
+
+https://sylabs.io/guides/3.5/user-guide/definition_files.html
+
+
+
+"Bootstrap" keyword
+-------------------
+
+Defines how we get the starting image
+
+* `library`: on Sylab Cloud container library
+* `docker`: Docker Hub
+  See: <https://sylabs.io/guides/3.5/user-guide/appendix.html#build-docker-module>
+
+See: <https://sylabs.io/guides/3.5/user-guide/definition_files.html#preferred-bootstrap-agents>
+
+
+https://cloud.sylabs.io/library