Clarify that releases does not require Autotools

Author: albinahlback

INSTALL

@@ -0,0 +1,60 @@
+# Instructions on installing FLINT
+
+## Building from release
+
+If building FLINT from a release (such as a tarball), one needs the following:
+
+* GMP (https://gmplib.org/)
+* MPFR (https://mpfr.org/)
+* Either of the following build systems:
+  * GNU Make
+  * CMake (Only supported for Windows users)
+
+Moreover, if user intends to use FLINT's assembly code, user needs to have the
+M4 preprocessor installed.
+
+One can install GMP, MPFR and GNU Make on a Ubuntu system via
+
+    apt install libgmp-dev libmpfr-dev make
+
+After this, FLINT should be ready to install, which can be done as follows:
+
+    ./configure
+    make -j
+    make install
+
+We also recommend that you run ``make check`` to check that the build was done
+correctly before installing.
+
+For a complete list of settings, write
+
+    ./configure --help
+
+An example of a custom configuration command would be
+
+    ./configure                                         \
+        --enable-assert                                 \
+        --disable-static                                \
+        --with-gmp-include=/home/user1/builds/includes/ \
+        --with-gmp-lib=/home/user1/builds/lib/          \
+        --with-mpfr=/usr                                \
+        --prefix=/home/user1/installations/             \
+        CC=clang                                        \
+        CFLAGS="-Wall -O3 -march=alderlake"
+
+For more information, see the FLINT documentation.
+
+## Building from scratch
+
+When building from scratch, one needs to generate the configuration script. For
+this, the user also needs to install GNU Autotools, which on a Ubuntu system can
+be done via
+
+    apt install autoconf libtool-bin
+
+After this, run
+
+    ./bootstrap.sh
+
+and FLINT should then be ready to be configured, built, checked and installed as
+described by the previous section.

INSTALL.md

@@ -11,16 +11,14 @@ Building FLINT requires:
 * GMP, at least version 6.2.1 (https://gmplib.org/)
 * MPFR, at least version 4.1.0 (https://mpfr.org/)
 * Either of the following build systems:
-
   * GNU Make together with GNU Autotools (Recommended)
-  * CMake (Recommended only for Windows users)
+  * CMake (Only supported for Windows users)
 
-On a typical Linux or Unix-like system where Autotools is available (see below
-for instructions using CMake), FLINT can be built and installed as follows:
+If building from a release on a typical Linux or Unix-like system (see below for
+instructions using CMake), FLINT can be configured, built and installed as follows:
 
 .. code-block:: bash
 
-    ./bootstrap.sh
     ./configure
     make -j N
     make install
@@ -29,6 +27,17 @@ where ``N`` is the number of jobs number allowed to run parallel. Typically, the
 fastest way to build is to let ``N`` be the number of threads your CPU plus one,
 which can be obtained in Bash through ``$(expr $(nproc) + 1)``.
 
+If building from scratch, that is, without a ``configure`` script, then ``configure``
+needs to be generated first. For this GNU Autotools needs to be installed in
+order to run
+
+.. code-block:: bash
+
+    ./bootstrap.sh
+
+After this is done, ``configure`` should be generated and user can proceed with
+configuring, building and installing FLINT.
+
 By default, FLINT only builds a shared library, but a static library can be
 built by pushing ``--enable-static`` to ``configure``.