Update readme with info from supermodule.

README.md

@@ -16,7 +16,7 @@ By [MoSHI](https://www.moshi.pitt.edu/), [University of Pittsburgh](https://www.
 
 For RAPIDS installation refer to to the [documentation](https://www.rapids.science/1.8/setup/installation/)
 
-## For the installation of the Docker version
+### For the installation of the Docker version
 
 1. Follow the [instructions](https://www.rapids.science/1.8/setup/installation/) to setup RAPIDS via Docker (from scratch).
 
@@ -62,7 +62,7 @@ Then follow the "cr-features module" section below.
     conda env export --no-builds | sed 's/^.*libgfortran.*$/  - libgfortran/' | sed 's/^.*mkl=.*$/  - mkl/' >  environment.yml
     ```
 
-## cr-features module 
+### cr-features module 
 
 This RAPIDS extension uses cr-features library accessible [here](https://repo.ijs.si/matjazbostic/calculatingfeatures).
 
@@ -79,3 +79,121 @@ To use cr-features library:
     cr-features package has to be built and installed everytime to get the newest version. 
     Or an the newest version of the docker image must be used.   
     ```
+
+## Updating RAPIDS
+
+To update RAPIDS, first pull and merge [origin]( https://github.com/carissalow/rapids), such as with:
+
+```commandline
+git fetch --progress "origin" refs/heads/master
+git merge --no-ff origin/master
+```
+
+Next, update the conda and R virtual environment.
+
+```bash
+R -e 'renv::restore(repos = c(CRAN = "https://packagemanager.rstudio.com/all/__linux__/focal/latest"))'
+```
+
+## Custom configuration
+### Credentials
+
+As mentioned under [Database in RAPIDS documentation](https://www.rapids.science/1.6/snippets/database/), a `credentials.yaml` file is needed to connect to a database.
+It should contain:
+
+```yaml
+PSQL_STRAW:
+  database: staw
+  host: 212.235.208.113
+  password: password
+  port: 5432
+  user: staw_db
+```
+
+where`password` needs to be specified as well.
+
+## Possible installation issues
+### Missing dependencies for RPostgres
+
+To install `RPostgres` R package (used to connect to the PostgreSQL database), an error might occur:
+
+```text
+------------------------- ANTICONF ERROR ---------------------------
+Configuration failed because libpq was not found. Try installing:
+   * deb: libpq-dev (Debian, Ubuntu, etc)
+   * rpm: postgresql-devel (Fedora, EPEL)
+   * rpm: postgreql8-devel, psstgresql92-devel, postgresql93-devel, or postgresql94-devel (Amazon Linux)
+   * csw: postgresql_dev (Solaris)
+   * brew: libpq (OSX)
+If libpq is already installed, check that either:
+  (i)  'pkg-config' is in your PATH AND PKG_CONFIG_PATH contains a libpq.pc file; or
+  (ii) 'pg_config' is in your PATH.
+If neither can detect , you can set INCLUDE_DIR
+and LIB_DIR manually via:
+  R CMD INSTALL --configure-vars='INCLUDE_DIR=... LIB_DIR=...'
+--------------------------[ ERROR MESSAGE ]----------------------------
+  <stdin>:1:10: fatal error: libpq-fe.h: No such file or directory
+compilation terminated.
+```
+
+The library requires `libpq` for compiling from source, so install accordingly.
+
+### Timezone environment variable for tidyverse (relevant for WSL2)
+
+One of the R packages, `tidyverse` might need access to the `TZ` environment variable during the installation.
+On Ubuntu 20.04 on WSL2 this triggers the following error:
+
+```text
+> install.packages('tidyverse')
+
+ERROR: configuration failed for package ‘xml2’
+System has not been booted with systemd as init system (PID 1). Can't operate.
+Failed to create bus connection: Host is down
+Warning in system("timedatectl", intern = TRUE) :
+  running command 'timedatectl' had status 1
+Error in loadNamespace(j <- i[[1L]], c(lib.loc, .libPaths()), versionCheck = vI[[j]]) :
+  namespace ‘xml2’ 1.3.1 is already loaded, but >= 1.3.2 is required
+Calls: <Anonymous> ... namespaceImportFrom -> asNamespace -> loadNamespace
+Execution halted
+ERROR: lazy loading failed for package ‘tidyverse’
+```
+
+This happens because WSL2 does not use the `timedatectl` service, which provides this variable.
+
+```bash
+~$ timedatectl
+System has not been booted with systemd as init system (PID 1). Can't operate.
+Failed to create bus connection: Host is down
+```
+
+and later 
+
+```bash 
+Warning message:
+In system("timedatectl", intern = TRUE) :
+  running command 'timedatectl' had status 1
+Execution halted
+```
+
+This can be amended by setting the environment variable manually before attempting to install `tidyverse`:
+
+```bash
+export TZ='Europe/Ljubljana'
+```
+
+## Possible runtime issues
+### Unix end of line characters
+
+Upon running rapids, an error might occur:
+
+```bash
+/usr/bin/env: ‘python3\r’: No such file or directory
+```
+
+This is due to Windows style end of line characters. 
+To amend this, I added a `.gitattributes` files to force `git` to checkout `rapids` using Unix EOL characters.
+If this still fails, `dos2unix` can be used to change them.
+
+### System has not been booted with systemd as init system (PID 1)
+
+See [the installation issue above](#Timezone-environment-variable-for-tidyverse-(relevant-for-WSL2)).