Dockerfile_alpine: fix broken pip six installation (OSGeo#1568)

Fixes docker hub error:

```
Step 32/49 : RUN pip3 install --upgrade pip six grass-session
---> Running in 1c63e0d56789
Collecting pip
Downloading pip-21.1.1-py3-none-any.whl (1.5 MB)
Collecting six
Downloading six-1.16.0-py2.py3-none-any.whl (11 kB)
Collecting grass-session
Downloading grass_session-0.5-py2.py3-none-any.whl (31 kB)
Installing collected packages: pip, six, grass-session
Attempting uninstall: pip
Found existing installation: pip 20.0.2
Uninstalling pip-20.0.2:
Successfully uninstalled pip-20.0.2
Attempting uninstall: six
Found existing installation: six 1.15.0
ERROR: Cannot uninstall 'six'. It is a distutils installed project and thus we cannot accurately determine which files belong to it which would lead to only a partial uninstall.
```

CONTRIBUTING.md

@@ -1,3 +1,24 @@
+# Introduction
+
+GRASS GIS is written in more than one programming language. While most
+of the source code is written in C, about 30% is written in Python. A
+compiler is needed to convert the C/C++ source code into executable
+files ("binaries"). In contrast, Python is an interpreted language that
+can only be executed with Python software.
+
+Now, in order to create an installable binary package from a source
+code package, the so-called "compilation step" is required. While the
+source code consists of thousands of C and Python files (plus HTML
+documentation), the included "makefiles" tell the build system to
+generate binaries from the source code in the correct order, render the
+manual pages, etc.
+
+The way to install the compiler tools and Python depends on the operating
+system. To make this easier, we have collected copy-paste instructions
+for most operating systems in our wiki:
+
+[Compile and install instructions](https://grasswiki.osgeo.org/wiki/Compile_and_Install)
+
 # Contributing
 
 There is more than one way of contributing to GRASS GIS.

docker/alpine/Dockerfile

@@ -2203,6 +2203,7 @@ FROM common as grass
 <<<<<<< HEAD
 <<<<<<< HEAD
 <<<<<<< HEAD
+<<<<<<< HEAD
 =======
 >>>>>>> main
 =======
@@ -2324,6 +2325,10 @@ FROM common as grass
 =======
 >>>>>>> 8422103f4c (wxpyimgview: explicit conversion to int (#2704))
 >>>>>>> osgeo-main
+=======
+<<<<<<< HEAD:docker/alpine/Dockerfile
+=======
+>>>>>>> b67db97c2e (Dockerfile_alpine: fix broken pip six installation (#1568))
 ENV LC_ALL="en_US.UTF-8"
 
 # Copy GRASS GIS from build image
@@ -2347,6 +2352,7 @@ COPY --from=build /usr/local/grass* /usr/local/grass/
 <<<<<<< HEAD
 <<<<<<< HEAD
 <<<<<<< HEAD
+<<<<<<< HEAD
 =======
 >>>>>>> main
 =======
@@ -2390,6 +2396,8 @@ COPY --from=build /usr/local/grass* /usr/local/grass/
 >>>>>>> osgeo-main
 =======
 >>>>>>> osgeo-main
+=======
+>>>>>>> b67db97c2e (Dockerfile_alpine: fix broken pip six installation (#1568))
 # pip 20.0.0 fix
 RUN apk add curl && curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py && python3 get-pip.py pip==20.0.2 && rm get-pip.py
 
@@ -2409,6 +2417,7 @@ RUN apk add curl && curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py && p
 <<<<<<< HEAD
 <<<<<<< HEAD
 <<<<<<< HEAD
+<<<<<<< HEAD
 =======
 >>>>>>> main
 <<<<<<< HEAD:docker/alpine/Dockerfile
@@ -2733,6 +2742,13 @@ RUN grass --tmp-location EPSG:4326 --exec g.version -rge && \
 =======
 >>>>>>> 8422103f4c (wxpyimgview: explicit conversion to int (#2704))
 >>>>>>> osgeo-main
+=======
+RUN pip3 install --upgrade grass-session
+
+RUN ln -s /usr/local/grass /usr/local/grass7
+RUN ln -s /usr/local/grass `grass --config path`
+RUN grass --tmp-location EPSG:4326 --exec g.version -rge && \
+>>>>>>> b67db97c2e (Dockerfile_alpine: fix broken pip six installation (#1568))
     pdal --version && \
     python3 --version
 
@@ -2763,6 +2779,7 @@ ENV GRASSBIN=grass
 <<<<<<< HEAD
 <<<<<<< HEAD
 <<<<<<< HEAD
+<<<<<<< HEAD
 =======
 >>>>>>> main
 =======
@@ -3008,6 +3025,13 @@ RUN grass --tmp-location EPSG:4326 --exec g.extension extension=r.learn.ml
 =======
 >>>>>>> 8422103f4c (wxpyimgview: explicit conversion to int (#2704))
 >>>>>>> osgeo-main
+=======
+RUN grass --tmp-location EPSG:4326 --exec g.extension extension=r.in.pdal
+RUN /usr/bin/python3 /scripts/test_grass_session.py
+
+# Test addon installation
+RUN grass --tmp-location EPSG:4326 --exec g.extension extension=r.learn.ml
+>>>>>>> b67db97c2e (Dockerfile_alpine: fix broken pip six installation (#1568))
 
 
 FROM grass as final
@@ -3030,6 +3054,7 @@ FROM grass as final
 <<<<<<< HEAD
 <<<<<<< HEAD
 <<<<<<< HEAD
+<<<<<<< HEAD
 =======
 >>>>>>> main
 =======
@@ -3081,6 +3106,9 @@ FROM grass as final
 =======
 >>>>>>> e526e86235 (Dockerfile_alpine: fix broken pip six installation (#1568)):docker/alpine/Dockerfile_alpine
 >>>>>>> 01018c1f62 (Dockerfile_alpine: fix broken pip six installation (#1568))
+=======
+>>>>>>> e526e86235 (Dockerfile_alpine: fix broken pip six installation (#1568)):docker/alpine/Dockerfile_alpine
+>>>>>>> b67db97c2e (Dockerfile_alpine: fix broken pip six installation (#1568))
 # GRASS GIS specific
 # allow work with MAPSETs that are not owned by current user
 <<<<<<< HEAD