remove mobi file format creation from makefile and explain it in README instead

doc/Makefile

@@ -22,7 +22,7 @@ endif
 SOURCES=$(wildcard src/*.txt)
 OBJECTS=$(SOURCES:src/%.txt=$(RSTDIR)/%.rst)
 
-.PHONY: help clean-all clean ebook html pdf old venv
+.PHONY: help clean-all clean epub html pdf old venv
 
 # ------------------------------------------
 
@@ -32,7 +32,7 @@ help:
 	@echo "  pdf        create Manual.pdf and Developer.pdf in this dir"
 	@echo "  old        create old-style HTML doc pages in old dir"
 	@echo "  fetch      fetch HTML and PDF files from LAMMPS web site"
-	@echo "  ebook      create ePUB/mobi file with manual in this dir"
+	@echo "  epub       create ePUB format manual for e-book readers"
 	@echo "  clean      remove all intermediate RST files"
 	@echo "  clean-all  reset the entire build environment"
 	@echo "  txt2html   build txt2html tool"
@@ -64,8 +64,9 @@ html: $(OBJECTS)
 	@rm -rf html/USER/*/*.[sg]*
 	@echo "Build finished. The HTML pages are in doc/html."
 
-ebook: $(OBJECTS)
+epub: $(OBJECTS)
 	@mkdir -p epub
+	@rm -f LAMMPS.epub
 	@cp src/JPG/lammps-logo.png epub/
 	@(\
 		. $(VENV)/bin/activate ;\
@@ -73,10 +74,9 @@ ebook: $(OBJECTS)
 		sphinx-build -j 8 -b epub -c utils/sphinx-config -d $(BUILDDIR)/doctrees $(RSTDIR) epub ;\
 		deactivate ;\
 	)
-	@-(cd epub; ebook-convert LAMMPS.epub LAMMPS.mobi )
-	@-mv -f epub/LAMMPS.epub epub/LAMMPS.mobi .
+	@mv  epub/LAMMPS.epub .
 	@rm -rf epub
-	@echo "Build finished. The ebook file(s) is/are created."
+	@echo "Build finished. The ePUB manual file is created."
 
 pdf: utils/txt2html/txt2html.exe
 	@(\

doc/README

 LAMMPS Documentation
 
 Depending on how you obtained LAMMPS, this directory has 2 or 3
-sub-directories and optionally 2 PDF files and 2 ebook files:
+sub-directories and optionally 2 PDF files and an ePUB file:
 
 src             content files for LAMMPS documentation
 html            HTML version of the LAMMPS manual (see html/Manual.html)
@@ -9,7 +9,6 @@ tools           tools and settings for building the documentation
 Manual.pdf      large PDF version of entire manual
 Developer.pdf   small PDF with info about how LAMMPS is structured
 LAMMPS.epub     Manual in ePUB format
-LAMMPS.mobi     Manual in mobi format (required for for Kindle)
 
 If you downloaded LAMMPS as a tarball from the web site, all these
 directories and files should be included.
@@ -51,9 +50,7 @@ make pdf          # generate 2 PDF files (Manual.pdf,Developer.pdf)
 make old          # generate old-style HTML pages in old dir via txt2html
 make fetch        # fetch HTML doc pages and 2 PDF files from web site
                   #   as a tarball and unpack into html dir and 2 PDFs
-make ebook        # generate e-book LAMMPS.epub in ePUB format using Sphinx 
-                  #   optionally convert it to mobi format (for Kindle
-                  #   readers, requires "ebook-convert" from Calibre)
+make epub         # generate LAMMPS.epub in ePUB format using Sphinx 
 make clean        # remove intermediate RST files created by HTML build
 make clean-all    # remove entire build folder and any cached data
 
@@ -101,17 +98,18 @@ Installing prerequisites for PDF build
 
 ----------------
 
-Installing prerequisites for ebook build
+Installing prerequisites for epub build
 
 ## ePUB
 
 Same as for HTML. This uses the same tools and configuration
 files as the HTML tree.
 
-## mobi
-
 For converting the generated ePUB file to a mobi format file
-(for e-book readers, that cannot read ePUB), you also need to have
-the 'ebook-convert' tool from the "calibre" software installed.
-http://calibre-ebook.com/
+(for e-book readers like Kindle, that cannot read ePUB), you
+also need to have the 'ebook-convert' tool from the "calibre"
+software installed. http://calibre-ebook.com/
+You first create the ePUB file with 'make epub' and then do:
+
+ebook-convert LAMMPS.epub LAMMPS.mobi