Recommend pybuild-deps package for generating requirements-build.txt

Our current solution for the users who want to build Python project from
source (without wheel distributions) is to generate
`requirements-build.txt` using our custom script that lives in Cachito
project [1].

Fortunately, there is an external package (repo) that provides more
robust solution that is tested and has a faster resolution time:
-> https://github.com/bruno-fs/pybuild-deps

Update the pip documentation to start referencing the package as a
preferred and recommend way to generate `requirements-build.txt`.

---
[1]: https://github.com/containerbuildsystem/cachito/blob/master/bin/pip_find_builddeps.py

Signed-off-by: Michal Šoltis <[email protected]>

docs/pip.md

@@ -432,80 +432,8 @@ but contains build dependencies rather than runtime dependencies.
 *Note: this file must contain all the transitive build dependencies of each of your transitive runtime dependencies
 (you are installing dependencies from source).*
 
-There's no great way to generate such a file. As far as we know, the best solution is pip-compile combined with this
-standalone script that lives in the old Cachito repo:
-[pip\_find\_builddeps.py](https://github.com/containerbuildsystem/cachito/blob/master/bin/pip_find_builddeps.py).
-
-#### Prerequisites
-
-Generate a [fully resolved requirements.txt](#requirementstxt)
-
-Get the script ([download](https://raw.githubusercontent.com/containerbuildsystem/cachito/master/bin/pip_find_builddeps.py)
-directly from Github, it has no runtime dependencies other than pip)
-
-If your project itself has build dependencies (typically defined in pyproject.toml), copy them to `requirements-build.in`.
-
-<details>
-<summary>Example: pyproject.toml build dependencies</summary>
-
-```toml
-# pyproject.toml
-[build-system]
-requires = ["pdm-pep517"]
-build-backend = "pdm.pep517.api"
-```
-
-Copy dependencies from build-system.requires:
-
-```requirements.txt
-# requirements-build.in
-pdm-pep517
-```
-
-</details>
-
-**Usage:**
-
-Run the `pip_find_builddeps.py` script and pip-compile the output:
-
-```shell
-pip_find_builddeps.py requirements.txt \
-  --append \
-  --only-write-on-update \
-  -o requirements-build.in
-
-pip-compile requirements-build.in --allow-unsafe --generate-hashes
-```
-
-<details>
-<summary>Result: requirements-build.txt</summary>
-
-```requirements.txt
-#
-# This file is autogenerated by pip-compile with Python 3.10
-# by the following command:
-#
-#    pip-compile --allow-unsafe --generate-hashes requirements-build.in
-#
-flit-core==3.8.0 \
-    --hash=sha256:64a29ec845164a6abe1136bf4bc5ae012bdfe758ed42fc7571a9059a7c80bd83 \
-    --hash=sha256:b305b30c99526df5e63d6022dd2310a0a941a187bd3884f4c8ef0418df6c39f3
-    # via -r requirements-build.in
-pdm-pep517==1.0.6 \
-    --hash=sha256:8ec0c13cbacc9b94a9820be7db9e513c81a48ebca0bb826eb743fb1b22d144a0 \
-    --hash=sha256:a4407703d50fa4d671383a354868b05a13060c1bf38264cbb5ddc9a73e4a1dc5
-    # via -r requirements-build.in
-setuptools==66.1.1 \
-    --hash=sha256:6f590d76b713d5de4e49fe4fbca24474469f53c83632d5d0fd056f7ff7e8112b \
-    --hash=sha256:ac4008d396bc9cd983ea483cb7139c0240a07bbc74ffb6232fceffedc6cf03a8
-    # via -r requirements-build.in
-wheel==0.38.4 \
-    --hash=sha256:965f5259b566725405b05e7cf774052044b1ed30119b5d586b2703aafe8719ac \
-    --hash=sha256:b60533f3f5d530e971d6737ca6d58681ee434818fab630c83a734bb10c083ce8
-    # via -r requirements-build.in
-```
-
-</details>
+We recommend the [pybuild-deps](https://pypi.org/project/pybuild-deps) package to generate the requirements-build.txt file.
+It will automatically generate build requirements from your requirements.txt file.
 
 *Adding a requirements-build.txt should not require changes in your build process. Pip should install the build
 dependencies automatically as needed, you don't have to install them explicitly. The purpose of requirements-build.txt