README describes the necessity of CFITSIO 3.41 or earlier added

Gnuastro 0.2.51 only builds with CFITSIO 3.41 or earlier. But this was
not described in the README file. With this commit, a note has been
added regarding the CFITSIO version.

This issue was raised by Alejandro Serrano Borlaff.

README

@@ -83,7 +83,8 @@ difference.
     https://zenodo.org/record/1163746/files/gnuastro-0.2.51-bc56.tar.gz
 
   To uncompress, build and install the Gnuastro tarball, follow the
-  instructions here:
+  instructions in the link below. Also see the description on the
+  necessary version of CFITSIO (one of Gnuastro's dependencies) below.
 
     https://www.gnu.org/software/gnuastro/manual/html_node/Quick-start.html
 
@@ -102,6 +103,18 @@ difference.
     https://www.gnu.org/software/gnuastro/manual/html_node/Bootstrapping.html
 
 
+  CFITSIO 3.41 or earlier
+  -----------------------
+
+  CFITSIO is one of Gnuastro's dependencies. But since version 3.42
+  (released after Gnuastro's version 0.2.51), it also depends on the
+  cURL library. So the configure script of Gnuastro 0.2.51 will fail
+  to link with CFITSIO 3.42 or above and thus complain that it can't
+  find it. CFITSIO version 3.41 can be downloaded from this link:
+
+    https://heasarc.gsfc.nasa.gov/FTP/software/fitsio/c/cfitsio3410.tar.gz
+
+
   AWK
   ---
 
@@ -165,4 +178,12 @@ difference.
 
   LaTeX is used to build the final PDF of this pipeline. Some
   important packages within LaTeX that this pipeline uses are:
-  `biblatex' and `pgfplots'.
\ No newline at end of file
+  `biblatex' and `pgfplots'.
+
+
+
+Acknowledgments
+===============
+
+  We would like to thank Alejandro Serrano Borlaff for comments
+  regarding the pipeline after its publication.
\ No newline at end of file