add note on basic datalad run and datalad rerun

notes.txt

@@ -16,3 +16,12 @@ states of a dataset: "datalad diff -f/--from COMMIT -t/--to COMMIT"
 and "git diff COMMIT COMMIT", where COMMIT is a shasum of a commit
 in the history.
 
+The datalad run command can record the impact a script or command has on a Dataset.
+In its simplest form, datalad run only takes a commit message and the command that
+should be executed.
+
+Any datalad run command can be re-executed by using its commit shasum as an argument
+in datalad rerun CHECKSUM. DataLad will take information from the run record of the original
+commit, and re-execute it. If no changes happen with a rerun, the command will not be written
+to history. Note: you can also rerun a datalad rerun command!
+