split HTML and PDF documentation build

"make doc" now only builds the HTML documentation, which is what most
people use. The PDF documentation is now built with "make docpdf"

CHANGELOG.md

@@ -32,6 +32,8 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - The logic in the configure script that determines the library-link flags for compilation on different systems has been simplified.   \[Rene Gassmoeller; 6-19-2024; [#534](https://github.com/geodynamics/Rayleigh/pull/534)\]
 
+- The documentation build has been split into HTML (`make doc`) and PDF (`make docpdf`) outputs.   \[Philipp Edelmann; 6-21-2024; [#552](https://github.com/geodynamics/Rayleigh/pull/552)\]
+
 ### Fixed
 
 - Rayleigh no longer attempts to update the record count and close a diagnostics file (e.g., G_Avgs) that failed to open correctly.  \[Nick Featherstone; 6-18-2024; [#510](https://github.com/geodynamics/Rayleigh/pull/510) , [#523](https://github.com/geodynamics/Rayleigh/pull/523)  \]

Makefile

@@ -91,6 +91,9 @@ endif
 .PHONY: doc
 doc:
 	@sphinx-build -M html "." "doc/build"
+
+.PHONY: docpdf
+doc:
 	@sphinx-build -M latexpdf "." "doc/build"
 
 .PHONY: distclean

doc/source/User_Guide/getting_started.rst

@@ -58,7 +58,7 @@ Building the documentation is the same on Linux and Mac.
     cd /path/to/Rayleigh
     make doc
 
-Once the documetation builds, you can access it by opening ``Rayleigh/doc/build/html/index.html`` in your web browser.
+Once the documetation builds, you can access it by opening ``Rayleigh/doc/build/html/index.html`` in your web browser. To build the PDF version of the documentation (same content as HTML) you run ``make docpdf``.
 
 Building the code is again the same on Linux and Mac. Execute the following: