README: Move the check out instructions to one place. (#1285)

README.md

@@ -78,7 +78,16 @@ appropriate for your platform.
 
 ### Via source code
 
-See below.
+Irrespective of the OS used, before building, check out the project and the
+necessary submodules:
+
+```sh
+git clone https://github.com/solvespace/solvespace
+cd solvespace
+git submodule update --init
+```
+
+You will need `git`. See the platform specific instructions below to install it.
 
 ## Building on Linux
 
@@ -105,13 +114,7 @@ sudo dnf install git gcc-c++ cmake zlib-devel libpng-devel \
             mesa-libGL-devel mesa-libGLU-devel libspnav-devel
 ```
 
-Before building, check out the project and the necessary submodules:
-
-```sh
-git clone https://github.com/solvespace/solvespace
-cd solvespace
-git submodule update --init extlib/libdxfrw extlib/mimalloc extlib/eigen
-```
+Before building, [check out the project and the necessary submodules](#via-source-code).
 
 After that, build SolveSpace as following:
 
@@ -145,13 +148,7 @@ Debian derivative (e.g. Ubuntu) these can be installed with:
 apt-get install git build-essential cmake mingw-w64
 ```
 
-Before building, check out the project and the necessary submodules:
-
-```sh
-git clone https://github.com/solvespace/solvespace
-cd solvespace
-git submodule update --init
-```
+Before building, [check out the project and the necessary submodules](#via-source-code).
 
 Build 64-bit SolveSpace with the following:
 
@@ -189,13 +186,7 @@ source ./emsdk_env.sh
 cd ..
 ```
 
-Before building, check out the project and the necessary submodules:
-
-```sh
-git clone https://github.com/solvespace/solvespace
-cd solvespace
-git submodule update --init
-```
+Before building, [check out the project and the necessary submodules](#via-source-code).
 
 After that, build SolveSpace as following:
 
@@ -225,13 +216,7 @@ brew install git cmake libomp
 XCode has to be installed via AppStore or [the Apple website][appledeveloper];
 it requires a free Apple ID.
 
-Before building, check out the project and the necessary submodules:
-
-```sh
-git clone https://github.com/solvespace/solvespace
-cd solvespace
-git submodule update --init
-```
+Before building, [check out the project and the necessary submodules](#via-source-code).
 
 After that, build SolveSpace as following:
 
@@ -269,13 +254,7 @@ These can be installed from the ports tree:
 pkg_add -U git cmake libexecinfo png json-c gtk3mm pangomm
 ```
 
-Before building, check out the project and the necessary submodules:
-
-```sh
-git clone https://github.com/solvespace/solvespace
-cd solvespace
-git submodule update --init extlib/libdxfrw extlib/mimalloc extlib/eigen
-```
+Before building, [check out the project and the necessary submodules](#via-source-code).
 
 After that, build SolveSpace as following:
 
@@ -301,9 +280,11 @@ or later is required.
 If gawk is in your path be sure it is a proper Windows port that can handle CL LF line endings.
 If not CMake may fail in libpng due to some awk scripts - issue #1228.
 
+Before building, [check out the project and the necessary submodules](#via-source-code).
+
 ### Building with Visual Studio IDE
 
-Check out the git submodules. Create a directory `build` in
+Create a directory `build` in
 the source tree and point cmake-gui to the source tree and that directory.
 Press "Configure" and "Generate", then open `build\solvespace.sln` with
 Visual C++ and build it.
@@ -315,9 +296,6 @@ First, ensure that `git` and `cl` (the Visual C++ compiler driver) are in your
 Visual Studio install. Then, run the following in cmd or PowerShell:
 
 ```bat
-git clone https://github.com/solvespace/solvespace
-cd solvespace
-git submodule update --init
 mkdir build
 cd build
 cmake .. -G "NMake Makefiles" -DCMAKE_BUILD_TYPE=Release
@@ -333,9 +311,6 @@ First, ensure that git and gcc are in your `$PATH`. Then, run the following
 in bash:
 
 ```sh
-git clone https://github.com/solvespace/solvespace
-cd solvespace
-git submodule update --init
 mkdir build
 cd build
 cmake .. -DCMAKE_BUILD_TYPE=Release