Copy doc_src to sphinx_doc_src and add a TOC

sphinx_doc_src/cmds/else.rst

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+\section else else - execute command if a condition is not met
+
+\subsection else-synopsis Synopsis
+\fish{synopsis}
+if CONDITION; COMMANDS_TRUE...; [else; COMMANDS_FALSE...;] end
+\endfish
+
+\subsection else-description Description
+
+`if` will execute the command `CONDITION`. If the condition's exit status is 0, the commands `COMMANDS_TRUE` will execute. If it is not 0 and `else` is given, `COMMANDS_FALSE` will be executed.
+
+
+\subsection else-example Example
+
+The following code tests whether a file `foo.txt` exists as a regular file.
+
+\fish
+if test -f foo.txt
+    echo foo.txt exists
+else
+    echo foo.txt does not exist
+end
+\endfish